Direct isolation of the functional human thymidine kinase gene with a cosmid shuttle vector

5-Substituted-2′-deoxyuridines as anti-HSV-1 Agents: Synthesis and Structure Activity Relationship

Nucleoside and pyrophosphate analogues are currently in use to treat infection with Human herpesvirus 1 (HSV-1). Both series of compounds exert their activity by inhibition of the viral DNA polymerase either directly, or after anabolic phosphorylation. As the X-ray structure of the viral-specific DNA polymerase is not known, it is difficult to design a nucleoside or non-nucleoside antiviral agent which specifically inhibits this enzyme. Therefore, alternative strategies have relied on extensive structure activity relationship studies of anti-HSV-1 agents in an endeavour to understand the essential structural requirements for activity and hence the design of drugs with increased selectivity. A virus-specific enzyme which plays a crucial role in the selective activation of nucleoside analogues is thymidine kinase. Present knowledge regarding the specificity of herpesvirus thymidine kinase for its 5-substituted-2′-deoxyuridine substrates is reviewed herein.

Transformation of Ulva mutabilis (Chlorophyta) by vector plasmids integrating into the genome

A method for the stable transformation of the green marine macroalga Ulva mutabilis was developed based on vector plasmids integrating into the genome. By combination of the expression signals (promoter, enhancer, and transcriptional termination sequences) of a chromosomal rbcS gene from U. mutabilis with the bleomycin resistance gene (ble) from Streptoalloteichus hindustanus, a dominant selectable marker gene was constructed for the preparation of a series of E. coli-U. mutabilis shuttle vector plasmids. Special vectors were prepared for the introduction and expression of foreign genes in Ulva, for insertional mutagenesis and gene tagging by plasmid integration into the genome, and for protein tagging by the green fluorescent protein, as well as tools for posttranscriptional gene silencing and cosmid cloning to prepare genomic gene libraries for mutant gene complementation. The vectors were successfully tested in pilot experiments, where they were efficiently introduced into Ulva gametes, zoospores or protoplasts of somatic blade cells by treatment with Ca(2+) -ions and polyethylene glycol under isotonic conditions at low ionic strength. The parthenogenetically propagated phleomycin-resistant transformants of the mutant slender (sl) and the wildtype (wt) were demonstrated to be carrying the plasmids randomly integrated into the chromosomes often as tandem repeat clusters.

Non-Viral Deoxyribonucleoside Kinases--Diversity and Practical Use

Deoxyribonucleoside kinases (dNKs) phosphorylate deoxyribonucleosides to their corresponding monophosphate compounds. dNks also phosphorylate deoxyribonucleoside analogues that are used in the treatment of cancer or viral infections. The study of the mammalian dNKs has therefore always been of great medical interest. However, during the last 20 years, research on dNKs has gone into non-mammalian organisms. In this review, we focus on non-viral dNKs, in particular their diversity and their practical applications. The diversity of this enzyme family in different organisms has proven to be valuable in studying the evolution of enzymes. Some of these newly discovered enzymes have been useful in numerous practical applications in medicine and biotechnology, and have contributed to our understanding of the structural basis of nucleoside and nucleoside analogue activation.

A cosmid for selecting genes by complementation in Aspergillus nidulans: Selection of the developmentally regulated yA locus

We constructed a 9.9-kilobase cloning vector, designated pKBY2, for isolating genes by complementation of mutations in Aspergillus nidulans. pKBY2 contains the bacteriophage lambda cos site, to permit in vitro assembly of phage particles; a bacterial origin of replication and genes for resistance to ampicillin and chloramphenicol, to permit propagation in Escherichia coli; the A. nidulans trpC(+) gene, to permit selection in Aspergillus; and a unique BamHI restriction site, to permit insertion of DNA fragments produced by digestion with restriction endonucleases BamHI, BglII, Mbo I, or Sau3A. We used this cosmid to form a quasirandom recombinant DNA library containing 35- to 40-kilobase DNA fragments from a wild-type strain of A. nidulans. DNA from this library transformed a yellow-spored (yA(-)) pabaA(-)trpC(-)Aspergillus strain (FGSC237) to trpC(+) at frequencies of approximately 10 transformants per mug of DNA. Three of approximately 1000 trpC(+)pabaA(-) colonies obtained were putative yA(+) transformants, because they produced wild-type (green) spores. DNA from each of the green-spored transformants contained pKBY2 sequences and DNA from two transformants transduced E. coli to ampicillin resistance following treatment in vitro with a lambda packaging extract. The cosmids recovered in E. coli had similar restriction patterns and both yielded trpC(+) transformants of A. nidulans FGSC237, 85% of which produced green spores. Several lines of evidence indicate that the recovered cosmids contain a wild-type copy of the yA gene.

Ethylnitrosourea-induced mutation and molecular analysis of transgenic mice containing the gpt shuttle vector

Novel transgenic mice were developed in order to study the in vivo mutagenesis. The transgenic mice carried pCGK shuttle vector, which contained the Escherichia coli gpt gene as a mutational target, the kanamycin-resistant gene (Kanr) and cos region derived from bacteriophage lambda. The shuttle vector can be recovered from the transgenic mouse genome into the gpt-deficient E. coli by an in vitro packaging method and is selectable as a Kanr phenotype. Mutations induced at the gpt gene can be easily detected with a selective agent, 6-thioguanine (6-TG). In the previous study, the pCGK shuttle vector was incorporated into Chinese hamster CHL/IU cells and the resultant transgenic cell line was shown to be a useful system to study in vitro mutagenesis at the gpt gene. Therefore, an advantage of the shuttle vector is that in vivo mutational data obtained from the transgenic mouse can be compared with those of transgenic cell line in vitro. A transgenic CD-1 mouse line, designated as #128, that carried approximately 50 copies of pCGK shuttle vectors, was selected among 4 transgenic mouse lines. To investigate the sensitivity of the #128 line, the transgenic mice were treated with a single intraperitoneal injection of 250 mg/kg of N-ethyl-N-nitrosourea (ENU) or with 50 mg kg-1 day-1 of ENU for 5 consecutive days, and bone marrow, spleen and liver were dissected to investigate their mutational responses. The background mutant frequency was between 18x10(-6) and 75x10(-6) among all tissues tested. ENU induced significant increases in the mutant frequency above the background level in all three tissues at 14 days after single or 5-day treatment with the chemical. The increases in the mutant frequencies in bone marrow, spleen and liver were 6.4- to 6.8-fold, 3.0- to 5.6-fold and 3.0- to 3.3-fold, respectively. The shuttle vector DNA was recovered from the bone marrow of both spontaneous and ENU-treated mice and the gpt gene was amplified by polymerase chain reaction. The amplified DNA was subject to DNA sequence analysis. Out of 79 spontaneous and 52 ENU-induced mutants, the gpt gene could be amplified from 28 spontaneous and 46 ENU-induced mutants. DNA sequence analysis showed that predominant mutations were identified as A:T to T:A transversions (22 out of 46 sequenced mutants) and G:C to A:T transitions (9/46) in ENU-induced mutants, whereas G:C to T:A transversions (7 out of 28 sequenced mutants) were predominant in spontaneous mutants. These results demonstrate that this transgenic mouse, in combination with the transgenic CHL/IU cell line, is a useful system to study in vivo and in vitro mutational events at the same target gene.

Deletion mapping and X inactivation analysis of a non-specific mental retardation gene at Xp21.3-Xp22.11

We report on deletion mapping and X inactivation analysis of a gene for X linked non-specific mental retardation (MRX) at Xp21.3-Xp22.11, on the basis of molecular studies in two families with Xp microdeletions involving the DAX-1 gene. In family A, mental retardation (MR) was profound in the older brother with an episode of adrenal crisis, severe in the younger brother with no episode of adrenal crisis, and mild to moderate in the sister and the mother with no signs of adrenal hypoplasia. In family B, MR was absent in the male patient with adrenal hypoplasia. Polymerase chain reaction for 16 loci in the middle of Xp showed that the brothers of family A had a small Xp deletion between DXS7182 and DXS1022, and that the patient of family B had a tiny Xp deletion between DXS319 and DXS1022. Microsatellite analysis for tetranucleotide repeats in the promoter region of the DAX-1 gene and Southern blotting for DAX-1 and DXS28 showed that the sister and the mother of family A were heterozygous for the interstitial deletion. X inactivation analysis for the methylation status of the AR gene and the HPRT gene indicated that the normal X and the deleted X chromosome underwent random X inactivation in both the sister and the mother. The results imply that an MRX gene subject to X inactivation is present in a roughly 4 Mb region between DXS7182 and DAX-1, and that reduced expression of the normal MRX gene caused by random X inactivation results in MR in carrier females.

Development of a novel CHL/IU cell line with an incorporated gpt shuttle vector for concurrent analysis of gene mutations and chromosome aberrations

A cosmid shuttle vector containing the target gene of Escherichia coli gpt coding xanthine-guanine phosphoribosyl transferase was constructed. The shuttle vector was designed to be rescued into the gpt-deficient Escherichia coli from Chinese hamster CHL/IU cells through an in vitro packaging method. Mutations occurred at the target gene can be detected with a selective agent, 6-thioguanine (6-TG). The shuttle vector was stably transfected into CHL/IU cells to give several cell lines containing copies of the shuttle vector in the chromosomes. Each cell line exhibited a characteristic rescue efficiency (0 to 1.9 x 10(5) CFU/microgram of genomic DNA) of the shuttle vector and spontaneous mutation frequency (3.9 x 10(-5) to over 10(-2)) at the 6-TG selection. One transgenic cell line (KN63), which showed a higher rescue efficiency and a low spontaneous mutation frequency, was selected and tested for the ability to respond to a genotoxic agent, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). MNNG increased both the mutation frequency at the target gene and the number of the cells with chromosome aberrations. DNA sequence analysis of 6-TG mutants showed that predominant mutations (10/14) were identified as G:C to A:T transitions in MNNG-induced mutants, whereas transversions were predominant (5/9) in spontaneous mutants. These results suggest that this transgenic CHL/IU cell line can be a useful tool for analyzing the relation between gene mutations and chromosome aberrations.

Impaired male sex development in an infant with molecularly defined partial 9p monosomy: implication for a testis forming gene(s) on 9p

This paper describes a genetically male infant with impaired male sex development and partial 9p monosomy. The external genitalia were ambiguous with microphallus (penile length at birth 10 mm, mean age matched normal length 29 mm (SD 5)), hypospadias, and hypoplastic scrotum. The tests were undescended and severely hypoplastic (testis size at 12 months of age, right 8 x 5 x 4 mm and left 4 x 3 x 2 mm; mean age matched normal size, length 18 mm (SD 2), width 11 mm (SD 1). Cytogenetic studies showed a 46,XY,del(9)(p23) karyotype in all the 30 peripheral lymphocytes and 20 skin fibroblasts examined. Microsatellite analysis for a total of 13 loci assigned to the 9p22-24 region showed that the deleted chromosome 9 was of paternal origin and was missing a region distal to D9S168. Southern blot analysis for D9S47 also confirmed the 9p deletion. The sequence of SRY was normal. The results provide further support for the previously proposed hypothesis that a gene(s) for testis formation is present on the distal part of 9p and indicate in molecular terms that the putative testis forming gene(s) resides in the region distal to D9S168.

Mental retardation in a boy with an interstitial deletion at Xp22.3 involving STS, KAL1, and OA1: implication for the MRX locus

Although genotype-phenotype correlations in male patients with various types of nullisomy for Xp22.3 have assigned a locus for X-linked mental retardation (MRX) to an approximately 3-Mb region between DXS31 and STS, the precise location has not been determined. In this paper, we describe a 14 7/12 year old Japanese boy with mental retardation and an interstitial deletion at Xp22.3 involving STS, KAL1, and OA1, and compare the deletion map with that of previously reported three familial male patients with low-normal intelligence and a similar interstitial deletion at Xp22.3. The results suggest that the MRX gene is further localized to the roughly 1.5-Mb region between DXS1060 and DXS1139.

Localization and ordering of acid alpha-glucosidase (GAA) and thymidine kinase (TK1) by fluorescence in situ hybridization

Genomic DNA clones of human acid alpha glucosidase (GAA) and thymidine kinase (TK1) were used to map the exact location and order of these genes on human chromosome 17. Both genes were localized to the 17q25-qter band (17q25.2-q25.3), with GAA distal to TK1. They were also shown to be, respectively, distal and proximal to an anonymous cosmid (cK17.71) previously mapped to this region.

Short stature in a girl with partial monosomy of the pseudoautosomal region distal to DXYS15: further evidence for the assignment of the critical region for a pseudoautosomal growth gene(s)

This report describes a 12 year 10 month old girl with short stature and a non-mosaic 46,X,Xp+ karyotype. Her height remained below −2 SD of the mean, and her predicted adult height (143 cm) was below her target height (155·5 cm) and target range (147·5 cm−163·5 cm). Cytogenetic and molecular studies showed that the Xp+ chromosome was formed by an inverted duplication of the Xp21.3−Xp22.33 segment and was missing about 700 kb of DNA from the pseudoautosomal region distal to DXYS15. The results provide further support for the previously proposed hypothesis that the region between DXYS20 and DXYS15 is the critical region for a pseudoautosomal growth gene(s).

Absent chondrodysplasia punctata in a male with an Xp terminal deletion involving the putative region for CDPX1 locus

This is a follow-up report on a male patient with a 46,Y,r(X) karyotype. Although he had no clinico-radiological features of X-linked recessive chondrodysplasia punctata (CDPX1), molecular studies revealed an Xp terminal deletion involving the putative region for the CDPX1 locus (PABX-DXS31). We suspect that the absence of CDPX1 may be attributable to the nature of the disease and the extreme short stature of the patient (mean -5.6 S.D.).

Immunocytochemical localization of c-erbB-2 protein in transitional cell carcinoma of the urinary bladder

The level of expression and cellular localization of the c-erbB-2 gene product in transitional cell carcinoma of the urinary tract is controversial. Analysis of the c-erbB-2 gene structure and comparison of its expression in the same cells by Southern, Northern and immunoblotting, and by immunocytochemistry minimize the errors of interpretation inherent in one technique. Such a 'correlative study' has been performed on tumours from 82 patients. c-erbB-2 gene amplification was detected in 14 per cent of initial tumours and was associated with grade (P < 0.001). Raised levels of mRNA were seen in those tumours with increased gene copy number and in 13 per cent of the remainder. Immunoblotting detected the expected 185 kD immunoreactive protein and a 155 kD protein associated with high gene copy number. Immunocytochemistry localized c-erbB-2 immunoreactivity to the cell membrane and cytoplasm, and the latter predominated. Four antibodies to c-erbB-2 (AB-3, 21N, pAb 1, and NCL CB11) were compared on contiguous sections of the same tumour and showed the same pattern of immunoreactivity. Similarly, analyses carried out in three independent laboratories identified the same cellular localization. Membrane and cytoplasmic immunoreactivity was demonstrated in all tumours with gene amplification or increased mRNA levels and in 40 per cent of the remaining tumours. We showed that immunocytochemistry requires careful standardization of techniques and quantitation between different groups. However, despite variations in the intensity of immunoreactivity, the total number of positive cells remained constant. Therefore quantitation must be based on the number of positive cells and, ideally, their immunoreactive content relative to normal and positive tissue controls.

Chromosomal localisation of a pseudoautosomal growth gene(s)

Although recent molecular studies in patients with sex chromosome aberrations are consistent with a growth gene(s) being present in the pseudoautosomal region (PAR), the precise location has not been determined. In this report, we describe a Japanese boy and his mother with an interstitial deletion in Xp22.3 and review the correlation between genotype and stature in six cases of partial monosomy of the PAR. The results indicate that the region from DXYS20 to DXYS15 is the critical region for the putative growth gene(s).

Amplification and over-expression of c-erbB-2 in transitional cell carcinoma of the urinary bladder

The structure and expression of the proto-oncogene c-erbB-2 was studied in 86 patients with transitional cell carcinoma. Initial tissue samples comprised 37 grade 1, 32 grade 2 and 13 grade 3 tumours and four cases of carcinoma in situ. At the time of this first tumour sample, amplification of the c-erbB-2 gene was demonstrated by Southern blotting in 1/37 grade 1, 5/32 grade 2 and 6/13 grade 3 tumours (0.005 less than P less than 0.01). Tumour 're-occurrences' were obtained from 23 of these patients on one or more occasions. Amplification was detected in re-occurrences from seven of these 23, none of whom showed amplification in the first tumour sample. DNA was also extracted from exfoliated cells in urine collected from five cases of carcinoma in situ and c-erbB-2 amplification was demonstrated in one of these. No gene amplification was identified in patients' lymphocytes, ten biopsies of normal urothelium and 22 various intravesical pathologies. Increased expression of c-erbB-2 mRNA correlated with amplification of the gene. In addition, raised levels of mRNA were seen in the absence of gene amplification in six tumours. Immunoblotting using the polyclonal antibody 21N, raised against the c-terminus of the c-erbB-2 protein demonstrated increased amounts of a 185 kD immunoreactive protein in tumours with increased c-erbB-2 gene copy number compared with control tissues. In some tumours with high c-erbB-2 gene copy number, a 155 kD immunoreactive protein not detected in controls was expressed at higher level than the 185 kD protein. Immunocytochemistry using a monoclonal antibody AB-3, raised against the c-terminus of the c-erbB-2 protein, showed a positive reaction in the cytoplasm and cell membrane of tumours with gene amplification and in 40% of tumours with no amplification. An association was found between c-erbB-2 amplification and over-expression and the development of tumour re-occurrences. We suggest that c-erbB-2 amplification and over-expression may provide a useful molecular marker in transitional cell carcinoma of the bladder and merits further investigation as a potential prognostic indicator.

Use of short oligonucleotides to screen cosmid libraries for clones containing G/C-rich sequences

We have developed a method to identify clones containing recognition sequences for enzymes that cut mammalian genomes infrequently by direct screening of genomic libraries. The degenerate oligonucleotide NNGCGGCCGCNN, in which the internal 8 bases correspond to the recognition sequence of Not I, was used to screen a cosmid library, and it led to a greater than 10-fold enrichment in the number of clones containing Not I sites. This technique permits the efficient identification of sufficient clones from a chromosome-specific library to allow the construction of a complete pulsed-field map of that chromosome and to assist in finding genes in genomic DNA.

Current approaches to the molecular and physiological basis of cystic fibrosis

Cystic fibrosis (CF) is the most common disease caused by a single gene abnormality within the caucasian population. Its severity of expression in homozygotes varies widely, and the disease involves multiple organ systems. During the past few years, major advances in CF research have been made. These advances have occurred primarily in the fields of physiology and molecular genetics. As a result of these advances, it is now generally accepted that the basic defect in CF is the inability of an epithelial chloride channel to respond to adrenergic stimulation in affected organs. The recent major breakthrough in CF research is the localization of the CF gene and identification of the mutation responsible for the majority of cases of CF. In this article, the evidence which has led to this conclusion, as well as possible mechanisms by which a mutation in a single codon can produce the CF defects are reviewed. Finally, new approaches to the characterization of the CF gene by complementation of the defect in immortal cell lines displaying the transport phenotype associated with CF are discussed.

Molecular complementation of a genetic marker in Dictyostelium using a genomic DNA library

We constructed a partial Sau3A Dictyostelium genomic DNA library in a shuttle vector that replicates extrachromosomally in Dictyostelium cells. This library was used to complement Dictyostelium strain HPS400, which lacks thymidylate synthase activity and requires exogenous thymidine for growth. We have used a modified high-frequency transformation protocol that allows the introduction of the library into a sufficient number of Dictyostelium cells to select complementing plasmids. Using this approach, we have isolated a gene (Thy1) that complements the thymidine growth requirement of HPS400. The gene encodes a 1.2-kilobase RNA and the derived amino acid sequence shows no homology to thymidylate synthase, a protein highly conserved throughout evolution, or any other protein sequence in the data base examined. Thy1 provides an important selectable marker for transforming Dictyostelium cells. In addition, this work suggests that it will be possible to isolate genes that are essential for developmental processes in Dictyostelium by complementation.

Genomic DNA with transformation-related activity and melanoma antigen expression

We have analyzed the mouse melanoma antigen with monoclonal antibodies established by syngeneic immunization. To further understand the structure of this antigen at a molecular level, we have cloned the genomic DNA controlling the expression of melanoma antigen by cosmid library transfection and a monoclonal antibody. In the process of analyzing this DNA fragment we found that it contained a gene related with transformation, which was proved by tumor formation in nude mice inoculated with NIH/3T3 transfectants of this DNA fragment. We discuss the structure of the gene product based on the deduced amino acid sequence of cDNA, which maps the genome bearing transformation-related activity.

Construction of a genetic map of human chromosome 17 by use of chromosome-mediated gene transfer

We used somatic-cell hybrids, containing as their only human genetic contribution part or all of chromosome 17, as donors for chromosome-mediated gene transfer. A total of 54 independent transfectant clones were isolated and analyzed by use of probes or isoenzymes for greater than 20 loci located on chromosome 17. By combining the data from this chromosome-mediated gene transfer transfectant panel, conventional somatic-cell hybrids containing well-defined breaks on chromosome 17, and in situ hybridization, we propose the following order for these loci: pter-(TP53-RNP2-D17S1)-(MYH2-MYH1)-D17Z 1-CRYB1-(ERBA1-GCSF-NGL)-acute promyelocytic leukemia breakpoint-RNU2-HOX2-(NGFR-COLIAI-MPO)-GAA-UM PH-GHC-TK1-GALK-qter. Using chromosome-mediated gene transfer, we have also regionally localized the random probes D17S6 to D17S19 on chromosome 17.

Structure of the human blood platelet membrane glycoprotein Ib alpha gene

The gene for human platelet glycoprotein Ib alpha-chain has been cloned from a genomic cosmid library using a partial cDNA clone as probe. 3530 bp were sequenced including the entire transcribed part, as well as additional 5' and 3' regions. A single intron was found 6 bp upstream of the ATG initiation codon. An exceptionally long exon was identical to the recently published cDNA sequence (1). The 5' upstream promoter region is atypical for eukaryotic genes with only a weak homology to the characteristic promoter consensus sequences. The 3' region contains two repetitive Alu elements, belonging to distinct subfamilies, connected by an oligo(dA) linker.

Method of genomic DNA cloning by the combination of cosmid shuttle vector and monoclonal antibody

We report here the strategy to isolate the DNA fragment of any species origin which encodes cell surface antigen by using cosmid library transfection and cell sortings with a monoclonal antibody. We took the mouse melanoma antigen defined by monoclonal antibody as a model system and rescued the genomic DNA by in vitro packaging, showing the feasibility of this procedure.

Sequences contained within the promoter of the human thymidine kinase gene can direct cell-cycle regulation of heterologous fusion genes

Recent evidence on the transcriptional regulation of the human thymidine kinase (TK) gene raises the possibility that cell-cycle regulatory sequences may be localized within its promoter. A hybrid gene that combines the TK 5' flanking sequence and the coding region of the bacterial neomycin-resistance gene (neo) has been constructed. Upon transfection into a hamster fibroblast cell line K12, the hybrid gene exhibits cell-cycle-dependent expression. Deletion analysis reveals that the region important for cell-cycle regulation is within -441 to -63 nucleotides from the transcriptional initiation site. This region (-441 to -63) also confers cell-cycle regulation to the herpes simplex virus thymidine kinase (HSVtk) promoter, which is not expressed in a cell-cycle manner. We conclude that the -441 to -63 sequence within the human TK promoter is important for cell-cycle-dependent expression.

Isolation of genomic DNA controlling mouse melanoma antigen defined by monoclonal antibody

We have isolated the genomic DNA controlling the expression of murine specific melanoma antigen by employing cosmid shuttle vector and monoclonal antibody. Transfection of the cosmid library derived from mouse melanoma cells into human melanomas and repeated cell sortings of the fluorescence-bright population enabled us to enrich the antigen-positive transfectants. We rescued a 34.8 kb DNA fragment from the transfectants by in vitro packaging and showed it to be responsible for the antigen expression. However, we noticed instability of the antigen expression when the selection pressure imposed by the cell sorting was removed. This seemed to be due to the fact that the insert DNA was preferentially deleted from this cosmid vector without loss of the vector sequence itself.

Control of thymidine kinase mRNA during the cell cycle

To investigate the mechanism which controls the onset of DNA synthesis, we examined the regulation of thymidine kinase (TK) and its mRNA in the cell cycle. TK activity provides a useful marker for the onset of the S phase in mammalian cells. The present analysis of regulation of TK mRNA in BALB/c 3T3 cells showed that (i) the increase in TK activity depended on the availability of TK mRNA, (ii) the level of TK mRNA between G0 and S increased more than 20-fold, (iii) the rate of run-on TK transcription increased at most 2- to 4-fold between the G0 and S phases, (iv) the half-life of TK mRNA was greater than 8 to 12 h in the S and M phases and decreased as cells entered quiescence, (v) the TK mRNA increase was fully blocked by inhibition of protein synthesis by only 60%, (vi) this inhibition was completely effective for up to about 10 h following serum addition and progressively much less effective when the drugs were added later. These results suggest that the appearance of TK mRNA at the beginning of the S phase in serum-stimulated 3T3 cells is controlled not only by the rate of gene transcription but importantly also by the decreased rate of mRNA degradation. Similar mechanisms may be involved in regulation of the onset of DNA synthesis and the increase in TK mRNA since both are controlled in a manner consistent with a requirement for a labile protein.

Control of thymidine kinase mRNA during the cell cycle

To investigate the mechanism which controls the onset of DNA synthesis, we examined the regulation of thymidine kinase (TK) and its mRNA in the cell cycle. TK activity provides a useful marker for the onset of the S phase in mammalian cells. The present analysis of regulation of TK mRNA in BALB/c 3T3 cells showed that (i) the increase in TK activity depended on the availability of TK mRNA, (ii) the level of TK mRNA between G0 and S increased more than 20-fold, (iii) the rate of run-on TK transcription increased at most 2- to 4-fold between the G0 and S phases, (iv) the half-life of TK mRNA was greater than 8 to 12 h in the S and M phases and decreased as cells entered quiescence, (v) the TK mRNA increase was fully blocked by inhibition of protein synthesis by only 60%, (vi) this inhibition was completely effective for up to about 10 h following serum addition and progressively much less effective when the drugs were added later. These results suggest that the appearance of TK mRNA at the beginning of the S phase in serum-stimulated 3T3 cells is controlled not only by the rate of gene transcription but importantly also by the decreased rate of mRNA degradation. Similar mechanisms may be involved in regulation of the onset of DNA synthesis and the increase in TK mRNA since both are controlled in a manner consistent with a requirement for a labile protein.

Genetic analysis of the human thymidine kinase gene promoter

The promoter of the human thymidine kinase gene was defined by DNA sequence and genetic analyses. Mutant plasmids with deletions extending into the promoter region from both the 5' and 3' directions were constructed. The mutants were tested in a gene transfer system for the ability to transform TK- cells to the TK+ phenotype. This analysis delimited the functional promoter to within an 83-base-pair region upstream of the mRNA cap site. This region contains sequences common to other eucaryotic promoters including G X C-rich hexanucleotides, a CAAT box, and an A X T-rich region. The CAAT box is in an inverted orientation and is part of a 9-base-pair sequence repeated twice in the promoter region. Comparison of the genomic sequence with the cDNA sequence defined the first exon of the thymidine kinase gene.

Structure and expression of the Chinese hamster thymidine kinase gene

My colleagues and I have cloned a nearly full-length Chinese hamster thymidine kinase (TK) cDNA in a lambda gt10 vector and characterized this cDNA by nucleotide sequencing. The hamster TK protein is encoded in this cDNA by a 702-base-pair open reading frame which specifies a 25,625-dalton protein closely homologous to the previously described human and chicken TK proteins. Using cDNA nucleotide sequence data in conjunction with sequence data derived from selected subclones of the hamster TK gene recombinant phage lambda HaTK.5, we have resolved the structure of the TK gene, finding the 1,219 base pairs of the cDNA sequence to be distributed through 11.2 kilobases of genomic DNA in at least seven exon segments. In addition, we have constructed a variety of Chinese hamster TK minigenes and exonuclease III-S1 derivatives of these genes which have permitted us to define the limits of the Chinese hamster TK gene promoter and demonstrate that efficient TK transformation of Ltk- cells by TK minigenes depends on the presence of both TK intervening sequences and sequences 3' to the site of mRNA polyadenylation.

Genetic determinants of growth phase-dependent and adenovirus 5-responsive expression of the Chinese hamster thymidine kinase gene are contained within thymidine kinase mRNA sequences

We have constructed a chimeric thymidine kinase (TK) minigene, pHe delta 6Ha, which combines the complete coding and 3' noncoding regions of a Chinese hamster TK cDNA with the promoter region and 5' untranslated region of the TK gene of herpes simplex virus type 1. We have transformed rat 4 cells to Tk+ with this gene and analyzed the pattern of TK gene expression in these transformants under various conditions of in vitro cell culture. We find that TK gene expression in these Tk+ transformants is growth phase dependent, responsive to adenovirus 5 infection, and indistinguishable in character under a variety of cell culture conditions from the pattern of TK gene expression in rat 4 cells transformed to Tk+ with the genomic Chinese hamster TK gene clone lambda HaTK.5. We are led to the conclusion that the genetic elements which mediate growth phase-dependent TK gene expression are contained entirely within the sequences of the mature cytoplasmic hamster TK mRNA.

Identification and nucleotide sequence of the thymidine kinase gene of Shope fibroma virus

The thymidine kinase (TK) gene of Shope fibroma virus (SFV), a tumorigenic leporipoxvirus, was localized within the viral genome with degenerate oligonucleotide probes. These probes were constructed to two regions of high sequence conservation between the vaccinia virus TK gene and those of several known eucaryotic cellular TK genes, including human, mouse, hamster, and chicken TK genes. The oligonucleotide probes initially localized the SFV TK gene 50 kilobases (kb) from the right terminus of the 160-kb SFV genome within the 9.5-kb BamHI-HindIII fragment E. Fine-mapping analysis indicated that the TK gene was within a 1.2-kb AvaI-HaeIII fragment, and DNA sequencing of this region revealed an open reading frame capable of encoding a polypeptide of 176 amino acids possessing considerable homology to the TK genes of the vaccinia, variola, and monkeypox orthopoxviruses and also to a variety of cellular TK genes. Homology matrix analysis and homology scores suggest that the SFV TK gene has diverged significantly from its counterpart members in the orthopoxvirus genus. Nevertheless, the presence of conserved upstream open reading frames on the 5' side of all of the poxvirus TK genes indicates a similarity of functional organization between the orthopoxviruses and leporipoxviruses. These data suggest a common ancestral origin for at least some of the unique internal regions of the leporipoxviruses and orthopoxviruses as exemplified by SFV and vaccinia virus, respectively.

Molecular cloning and structural analysis of murine thymidine kinase genomic and cDNA sequences

Two functional cytosolic thymidine kinase (tk) cDNA clones were isolated from a mouse L-cell library. An RNA blot analysis indicated that one of these clones contains a nearly full-length tk sequence and that LTK- cells contain little or no TK message. The nucleotide sequences of both clones were determined, and the functional mouse tk cDNA contains 1,156 base pairs. An analysis of the sequence implied that there is an untranslated 32-nucleotide region at the 5' end of the mRNA, followed by an open reading frame of 699 nucleotides. The 3' untranslated region is 422 nucleotides long. Thus, the gene codes for a protein containing 233 amino acids, with a molecular weight of 25,873. A comparison of the coding sequences of the mouse tk cDNA with the human and chicken tk genes revealed about 86 and 70% homology, respectively. We also isolated the tk gene from a mouse C57BL/10J cosmid library. The structural organization was determined by restriction mapping, Southern blotting, and heteroduplex analysis of the cloned sequences, in combination with a mouse tk cDNA. The tk gene spans approximately 11 kilobases and contains at least five introns. Southern blot analysis revealed that this gene is deleted in mouse LTK- cells, consistent with the inability of these cells to synthesize TK message. This analysis also showed that tk-related sequences are present in the genomes of several mouse strains, as well as in LTK- cells. These segments may represent pseudogenes.

Genetic analysis of the human thymidine kinase gene promoter

The promoter of the human thymidine kinase gene was defined by DNA sequence and genetic analyses. Mutant plasmids with deletions extending into the promoter region from both the 5' and 3' directions were constructed. The mutants were tested in a gene transfer system for the ability to transform TK- cells to the TK+ phenotype. This analysis delimited the functional promoter to within an 83-base-pair region upstream of the mRNA cap site. This region contains sequences common to other eucaryotic promoters including G X C-rich hexanucleotides, a CAAT box, and an A X T-rich region. The CAAT box is in an inverted orientation and is part of a 9-base-pair sequence repeated twice in the promoter region. Comparison of the genomic sequence with the cDNA sequence defined the first exon of the thymidine kinase gene.

Genetic determinants of growth phase-dependent and adenovirus 5-responsive expression of the Chinese hamster thymidine kinase gene are contained within thymidine kinase mRNA sequences

We have constructed a chimeric thymidine kinase (TK) minigene, pHe delta 6Ha, which combines the complete coding and 3' noncoding regions of a Chinese hamster TK cDNA with the promoter region and 5' untranslated region of the TK gene of herpes simplex virus type 1. We have transformed rat 4 cells to Tk+ with this gene and analyzed the pattern of TK gene expression in these transformants under various conditions of in vitro cell culture. We find that TK gene expression in these Tk+ transformants is growth phase dependent, responsive to adenovirus 5 infection, and indistinguishable in character under a variety of cell culture conditions from the pattern of TK gene expression in rat 4 cells transformed to Tk+ with the genomic Chinese hamster TK gene clone lambda HaTK.5. We are led to the conclusion that the genetic elements which mediate growth phase-dependent TK gene expression are contained entirely within the sequences of the mature cytoplasmic hamster TK mRNA.

Structure and expression of the Chinese hamster thymidine kinase gene

My colleagues and I have cloned a nearly full-length Chinese hamster thymidine kinase (TK) cDNA in a lambda gt10 vector and characterized this cDNA by nucleotide sequencing. The hamster TK protein is encoded in this cDNA by a 702-base-pair open reading frame which specifies a 25,625-dalton protein closely homologous to the previously described human and chicken TK proteins. Using cDNA nucleotide sequence data in conjunction with sequence data derived from selected subclones of the hamster TK gene recombinant phage lambda HaTK.5, we have resolved the structure of the TK gene, finding the 1,219 base pairs of the cDNA sequence to be distributed through 11.2 kilobases of genomic DNA in at least seven exon segments. In addition, we have constructed a variety of Chinese hamster TK minigenes and exonuclease III-S1 derivatives of these genes which have permitted us to define the limits of the Chinese hamster TK gene promoter and demonstrate that efficient TK transformation of Ltk- cells by TK minigenes depends on the presence of both TK intervening sequences and sequences 3' to the site of mRNA polyadenylation.

DNA-mediated transfer of cAMP resistance in CHO cells

Chinese hamster ovary (CHO) strain 10215 carries a dominant mutation which confers resistant to cAMP by virtue of an altered catalytic subunit of the cAMP-dependent protein kinase (Evain et al., 1979). This mutation was transferred to wild-type CHO cells by DNA-mediated gene transfer. Based on the absence of cAMP growth inhibition, seven transformant colonies were isolated. One of these, 11586, was studied in detail. This transformant showed the same phenotype as the mutant, including resistance to the morphological changes and growth inhibitory effects of 1 mM 8-Br-cAMP, reduced total cAMP dependent protein kinase activity and lowered sensitivity of the kinase to cAMP activation. When the cAMP-dependent protein kinase was fractionated on a DEAE-cellulose column, the transformant was lacking in type II cAMP dependent protein activity, to the same degree as the mutant. The transformant and mutant, but not wild-type cells, also failed to phosphorylate a 52,000-dalton protein in a cAMP-dependent manner. These characteristics support the conclusion that the gene for the mutant cAMP-dependent protein kinase has been transferred. The ability to transfer this gene by DNA-mediated transfer suggests that this methodology may be useful for the molecular isolation of the gene encoding the catalytic subunit of cAMP-dependent protein kinase.

Detection and analysis of UV-induced mutations in mammalian cell DNA using a lambda phage shuttle vector

In order to study mutagenesis in mammalian cells, stable mouse L-cell lines were established with multiple copies of a lambda phage vector that contains the supF gene of Escherichia coli as a target for mutagenesis. Rescue of viable phage from high molecular weight mouse cell DNA using lambda in vitro packaging extracts was efficient (5 phage per microgram of cell DNA per copy) and yielded a negligible background of mutant phage (0 out of 54,605). From mouse cells exposed to 254-nm ultraviolet light (12J/m2), 78,510 phage were rescued, of which 8 were found to have mutant supF genes. DNA sequence analysis of the mutants suggests that the primary site of UV mutagenesis in mammalian cells is at pyrimidine-cytosine (Y-C) sequences, and that the most frequent mutation at this site is a C----T transition.

Molecular cloning and structural analysis of murine thymidine kinase genomic and cDNA sequences

Two functional cytosolic thymidine kinase (tk) cDNA clones were isolated from a mouse L-cell library. An RNA blot analysis indicated that one of these clones contains a nearly full-length tk sequence and that LTK- cells contain little or no TK message. The nucleotide sequences of both clones were determined, and the functional mouse tk cDNA contains 1,156 base pairs. An analysis of the sequence implied that there is an untranslated 32-nucleotide region at the 5' end of the mRNA, followed by an open reading frame of 699 nucleotides. The 3' untranslated region is 422 nucleotides long. Thus, the gene codes for a protein containing 233 amino acids, with a molecular weight of 25,873. A comparison of the coding sequences of the mouse tk cDNA with the human and chicken tk genes revealed about 86 and 70% homology, respectively. We also isolated the tk gene from a mouse C57BL/10J cosmid library. The structural organization was determined by restriction mapping, Southern blotting, and heteroduplex analysis of the cloned sequences, in combination with a mouse tk cDNA. The tk gene spans approximately 11 kilobases and contains at least five introns. Southern blot analysis revealed that this gene is deleted in mouse LTK- cells, consistent with the inability of these cells to synthesize TK message. This analysis also showed that tk-related sequences are present in the genomes of several mouse strains, as well as in LTK- cells. These segments may represent pseudogenes.

Induction of cellular thymidine kinase occurs at the mRNA level

The thymidine kinase (TK) gene has been isolated from human genomic DNA. The gene was passaged twice by transfection of LTK- cells with human chromosomal DNA, and genomic libraries were made in lambda Charon 30 from a second-round TK+ transformant. When the library was screened with a human Alu probe, seven overlapping lambda clones from the human TK locus were obtained. None of the seven contained a functional TK gene as judged by transfection analysis, but several combinations of clones gave rise to TK+ colonies when cotransfected into TK- cells. A functional cDNA clone encoding the human TK gene has also been isolated. Using this cDNA clone as a probe in restriction enzyme/blot hybridization analyses, we have mapped the coding sequences and direction of transcription of the gene. We have also used a single-copy subclone from within the coding region to monitor steady-state levels of TK mRNA in serum-stimulated and simian virus 40-infected simian CV1 tissue culture cells. Our results indicate that the previously reported increase in TK enzyme levels seen after either treatment is paralleled by an equivalent increase in the steady-state levels of TK mRNA. In the case of simian virus 40-infected cells, the induction was delayed by 8 to 12 h, which is the length of time after infection required for early viral protein synthesis. In both cases, induction of TK mRNA coincides with the onset of DNA synthesis, but virally infected cells ultimately accumulate more TK mRNA than do serum-stimulated cells.

Induction of cellular thymidine kinase occurs at the mRNA level

The thymidine kinase (TK) gene has been isolated from human genomic DNA. The gene was passaged twice by transfection of LTK- cells with human chromosomal DNA, and genomic libraries were made in lambda Charon 30 from a second-round TK+ transformant. When the library was screened with a human Alu probe, seven overlapping lambda clones from the human TK locus were obtained. None of the seven contained a functional TK gene as judged by transfection analysis, but several combinations of clones gave rise to TK+ colonies when cotransfected into TK- cells. A functional cDNA clone encoding the human TK gene has also been isolated. Using this cDNA clone as a probe in restriction enzyme/blot hybridization analyses, we have mapped the coding sequences and direction of transcription of the gene. We have also used a single-copy subclone from within the coding region to monitor steady-state levels of TK mRNA in serum-stimulated and simian virus 40-infected simian CV1 tissue culture cells. Our results indicate that the previously reported increase in TK enzyme levels seen after either treatment is paralleled by an equivalent increase in the steady-state levels of TK mRNA. In the case of simian virus 40-infected cells, the induction was delayed by 8 to 12 h, which is the length of time after infection required for early viral protein synthesis. In both cases, induction of TK mRNA coincides with the onset of DNA synthesis, but virally infected cells ultimately accumulate more TK mRNA than do serum-stimulated cells.