The protein encoded by a murine male germ cell-specific transcript is a putative ATP-dependent RNA helicase

Mouse erythroid cells express multiple putative RNA helicase genes exhibiting high sequence conservation from yeast to mammals

RNA secondary structure is a critical determinant of RNA function in ribosome assembly, pre-mRNA splicing, mRNA translation and RNA stability. The 'DEAD/H' family of putative RNA helicases may help regulate these processes by utilizing intrinsic RNA-dependent ATPase activity to catalyze conformational changes in RNA secondary structure. To investigate the repertoire of DEAD/H box proteins expressed in mammals, we used PCR techniques to clone from mouse erythroleukemia (MEL) cells three new DEAD box cDNAs with high similarity to known yeast (Saccharomyces cerevisiae) genes. mDEAD2 and mDEAD3 (mouse DEAD box proteins) are > 95% identical to mouse PL10 but exhibit differential tissue-specific expression patterns; mDEAD2 and mDEAD3 are also approx. 70% identical (at the aa level) to yeast DED1 and DBP1 proteins. Members of this DEAD box subclass contain C-terminal domains with high content of Arg, Ser, Gly and Phe, reminiscent of the RS domain in several Drosophila and mammalian splicing factors. mDEAD5 belongs to a second class related to translation initiation factors from yeast (TIF1/TIF2) and mammals (eIF-4A); this class contains a novel conserved peptide motif not found in other DEAD box proteins. Northern blotting shows that mDEAD5 is differentially expressed in testis vs. somatic tissues. Thus, mouse erythroid cells produce two highly conserved families of putative RNA helicases likely to play important roles in RNA metabolism and gene expression.

A human DEAD box protein with partial homology to heterogeneous nuclear ribonucleoprotein U

In a previous report, we showed that a novel DEAD box protein-encoding gene, DDX1, was amplified in two retinoblastoma (RB) cell lines. In addition to the eight conserved motifs that characterize all DEAD box proteins, the deduced amino acid sequence of DDX1 contains a subregion with considerable homology to heterogeneous nuclear ribonucleoprotein U.

Germ-line determination in Caenorhabditis and Ascaris: Will a helicase begin to unravel the mystery?

How cell lineages are established during development in higher eukaryotes is being addressed by geneticists and by developmental and molecular biologists. In Drosophila melanogaster, a gene corresponding to a germ-line-specific RNA helicase, vasa, has been shown to be a component o f the posteriorly localized germ granules o f the developing embryo. A putative RNA helicase, glh-I r which appears germ-line specific in its expression, has recently been reported from the free-living nematode Caenorhabditis elegans. Parasitologists studying the nematode Ascaris lumbricoides var. suum have found it to be a useful complement to Caenorhabditis. Deborah Roussell, Michael Gruidl and Karen Bennett predict that Ascaris will be valuable in determining the role played by germ-line helicases in development.

glh-1, a germ-line putative RNA helicase from Caenorhabditis, has four zinc fingers

We have cloned a family of putative RNA helicases from the free-living nematode Caenorhabditis elegans. One of these, a cDNA that we call glh-1, most closely matches in sequence and expression the previously described germ-line helicases PL10 from mouse and vasa from Drosophila. The amino terminus of the predicted protein of glh-1 contains a set of glycine-rich repeats similar in location and sequence to those in the predicted vasa protein. However, unlike all other putative RNA helicases, glh-1 also contains four retroviral-type zinc fingers. The RNA expression pattern of this Caenorhabditis helicase correlates with the presence of germ-line tissue in the parasitic nematode Ascaris lumbricoides var. suum and with the presence of germ cells in wild type and several germ-line mutants of Caenorhabditis. In the germ-line mutants glp-4 and glp-1, additional larger species of glh-1 RNA exist, which correspond to different adenylylated forms of the glh-1 transcript; these may be specified by motifs in the 3' untranslated region of glh-1 that are similar to adenylylation control elements and nos response elements.

Amplification of a DEAD box protein gene in retinoblastoma cell lines

DEAD box proteins, characterized by the conserved motif Asp-Glu-Ala-Asp, are putative RNA helicases implicated in a number of cellular processes involving alteration of RNA secondary structure such as translation initiation, nuclear and mitochondrial splicing, and ribosome and spliceosome assembly. Based on their distribution patterns, some members of this family are believed to be involved in embryogenesis, spermatogenesis, and cellular growth and division. Here, we report that the mRNA encoding a DEAD box protein, designated HuDBP-RB, is present at elevated levels in two of six retinoblastoma (RB) cell lines tested and is preferentially expressed in fetal tissues of neuroectodermal origin. It is not possible to classify HuDBP-RB as a member of any of the DEAD box protein subgroups identified to date since the regions of amino acid similarity between HuDBP-RB and other DEAD box proteins are restricted to the conserved motifs found in all members of this family. The HuDBP-RB gene, which has been mapped to chromosome band 2p24, is amplified in the RB cell lines that overexpress HuDBP-RB RNA. Furthermore, the MYCN gene is also present in multiple copies in these two cell lines, suggesting coamplification of the two genes.

comF, a Bacillus subtilis late competence locus, encodes a protein similar to ATP-dependent RNA/DNA helicases

We have sequenced and genetically characterized comF, a Bacillus subtilis competence locus, previously identified by Tn917 transposon insertion mutagenesis. Expression of the locus, in which three open reading frames (ORFs) were found, is driven by a single sigma A-like promoter in front of comFORF1 and is dependent on early regulatory competence genes and only expressed in competence medium. The predicted amino acid sequences of two of the ORFs showed similarities to known proteins in the GenBank and SwissProt databases: ComFORF1 is similar to an extensive family of ATP-dependent RNA/DNA helicases with closer similarity to the DEAD protein subfamily and to the PriA protein in Escherichia coli. The latter is a DNA translocase/helicase required for primosome assembly at the replication fork of phage phi X174. ComFORF3 is 22% identical to Com101, a protein required for genetic competence in Haemophilus influenzae, a naturally competent Gram-negative bacterium. In-frame comFORF1 deletions were 1000-fold deficient in transformability compared to the wild-type, whereas disruptions of the other two ORFs were only five- to 10-fold lower. These observations allow us to hypothesize that the ComFORF1 late gene product plays an essential role during the binding and uptake events involved in Bacillus subtilis transformation.

A yeast gene encoding a putative RNA helicase of the "DEAD"-box family

An unknown open reading frame from Saccharomyces cerevisiae was identified and sequenced. The predicted amino acid sequence shows high homology to the DEAD-box family of proteins. Gene disruption revealed that the gene is not essential for yeast but necessary for normal cell growth.

The Rad3 protein from Saccharomyces cerevisiae: a DNA and DNA:RNA helicase with putative RNA helicase activity

The Rad3 protein from Saccharomyces cerevisiae is a DNA helicase which participates in the repair of ultraviolet-irradiated DNA and is inhibited in the presence of DNA containing thymine dimers. This protein is also involved in mitotic recombination and spontaneous mutagenesis and is essential for cell viability in the absence of DNA damage. Furthermore, the Rad3 protein also exhibits a DNA:RNA helicase activity in which there is a significant preference for a partial DNA:RNA hybrid rather than a partial duplex DNA substrate, which suggests that this protein might be involved in DNA repair within transcriptionally active genes. Finally, the Rad3 protein contains the DEAH motif and shares high amino acid sequence similarity with the DEAD family of RNA helicase proteins, suggesting that it might also possess an RNA helicase activity.

High-level expression in male germ cells of murine P68 RNA helicase mRNA

The complete cDNA coding for mouse P68 RNA helicase was cloned and its nucleotide sequence was determined. The sequence is about 95% identical to the human equivalent. Whereas the 5'-untranslated region is less conserved (71%), the 3'-ends of mouse and human mRNAs are nearly identical. Between stop codon and poly(A)-tail both sequences are 97% conserved. At the level of amino acid sequence, the similarity of both, mouse and human, DEAD box family proteins is as high as 98%. In situ hybridizations using cDNA subfragments as probes revealed a testis-selective expression of P68 RNA helicase mRNA. The signal was restricted to late pachytene spermatocytes and haploid spermatids. Northern blot analyses corroborated these results but suggested that expression of related mRNA species occurs in a variety of other tissues.

In situ localization of male germ cell-associated kinase (mak) mRNA in adult mouse testis: specific expression in germ cells at stages around meiotic cell division

Biochemical analysis of the male germ cell-associated kinase (mak) gene, which was isolated recently by using weak cross-hybridization with the v-ros tyrosine kinase gene, revealed that the gene was highly expressed in mammalian testicular germ cells, but not in ovarian cells. In order to identify the cells which express the mak gene in more detail, we localized mak mRNA in frozen sections of mouse testis by non-radioactive in situ hybridization. In this study, we utilized thymine-thymine (T-T) dimerized mak cDNA as a haptenic, non-radioactive probe, and the signal was detected enzyme-immunohistochemically by using an anti-T-T antibody. As a result, mak mRNA was localized intensely in late pachytene (stage X) and diplotene (stage XI) spermatocytes, and faintly in dividing spermatocytes (stage XII) and early round spermatids (stage I-II), suggesting that the gene may play an important role in the phase around meiotic cell division, but not throughout the entire meiosis.

Characterization of male meiotic germ cell-specific antigen (Meg 1) by monoclonal antibody TRA 369 in mice

We have identified a male meiotic germ cell-specific antigen (Meg 1) with monoclonal antibody (mAb) TRA 369 in mice. The Meg 1 antigen was strongly expressed in specific steps of meiotic germ cells from pachytene spermatocyte to early spermatid, and not in other germ cells or somatic cells. Immunohistochemical examination revealed that the antigen was localized to the cytoplasm and was not distributed in the nucleus or on the cell surface. This antigen was demonstrated to have a molecular weight of 93 kDa and an isoelectric point of 5.2 by Western blotting. This molecule was first detected in the testis of 13-day-old mouse when pachytene spermatocytes first appeared. Thus this is a differentiation-specific antigen in male meiotic germ cells, and mAb TRA 369 is a useful tool to study the regulation of germ cell differentiation and to define germ cell development in a molecular level.

Expression of a mouse zinc finger protein gene in both spermatocytes and oocytes during meiosis

In order to identify genes regulating meiosis, a mouse spermatocyte cDNA library was screened for sequences encoding proteins with C2H2-type zinc finger motifs which are typically expressed by the Drosophila Krüppel gene. Three new cDNAs were isolated, and they were designated CTfin33, CTfin51, and CTfin92. Among them, CTfin51 was selected for further study. The deduced amino acid sequence revealed seven zinc finger motifs in its C-terminal region. Northern blot and in situ hybridization showed CTfin51 mRNA expression in spermatocytes after the pachytene stage and in early stage round spermatids of prepuberal and adult males. Immunocytochemical staining with an antiserum against beta-gal-CTfin51 fusion protein was localized within nuclei of spermatocytes and spermatids. Oocyte nuclei after the pachytene stage also were immunoreactive for CTfin51 protein. Immunoblots revealed a band at M(r) 75,000 in protein extracts from the testis and the ovary. These results suggest that the CTfin51 gene encodes a DNA-binding regulatory protein functionally associated with meiosis in both male and female gametogenesis.

Analysis of the Escherichia coli genome: DNA sequence of the region from 84.5 to 86.5 minutes

The DNA sequence of 91.4 kilobases of the Escherichia coli K-12 genome, spanning the region between rrnC at 84.5 minutes and rrnA at 86.5 minutes on the genetic map (85 to 87 percent on the physical map), is described. Analysis of this sequence identified 82 potential coding regions (open reading frames) covering 84 percent of the sequenced interval. The arrangement of these open reading frames, together with the consensus promoter sequences and terminator-like sequences found by computer searches, made it possible to assign them to proposed transcriptional units. More than half the open reading frames correlated with known genes or functions suggested by similarity to other sequences. Those remaining encode still unidentified proteins. The sequenced region also contains several RNA genes and two types of repeated sequence elements were found. Intergenic regions include three "gray holes," 0.6 to 0.8 kilobases, with no recognizable functions.

Dbp73D, a Drosophila gene expressed in ovary, encodes a novel D-E-A-D box protein

Proteins of the D-E-A-D family of putative ATP-dependent RNA helicases have been implicated in translation initiation and RNA splicing in a variety of organisms from E. coli to man. The Drosophila vasa protein, a member of this family, is required in the female germ line for fertility and for specification of germ line and posterior positional information in progeny embryos. We report the isolation of another D-E-A-D gene from Drosophila, which, like vasa, is expressed in germ line tissue. The predicted amino acid sequence of this new gene, Dbp73D, contains all of the highly conserved helicase motifs, but is otherwise the farthest-diverged member of the family so far identified.

Cloning, expression and localization of an RNA helicase gene from a human lymphoid cell line with chromosomal breakpoint 11q23.3

A gene encoding a putative human RNA helicase, p54, has been cloned and mapped to the band q23.3 of chromosome 11. The predicted amino acid sequence shares a striking homology (75% identical) with the female germline-specific RNA helicase ME31B gene of Drosophila. Unlike ME31B, however, the new gene expresses an abundant transcript in a large number of adult tissues and its 5' non-coding region was found split in a t(11;14)(q23.3;q32.3) cell line from a diffuse large B-cell lymphoma.

D-E-A-D protein family of putative RNA helicases

RNA metabolism plays a central role in cell growth. It is essential to regulate RNA synthesis, processing, stability and degradation. Conformational changes in RNA are key elements in regulating cellular processes. Recently, an increasing number of putative RNA helicases from different organisms ranging from Escherichia coli to humans and viruses have been identified. They are involved in diverse cellular functions such as RNA splicing, ribosome assembly, initiation of translation, spermatogenesis, embryogenesis, and cell growth and division. Based on sequence homologies these proteins were grouped in a family, the D-E-A-D box protein family (D-E-A-D = Asp-Glu-Ala-Asp). Some of the better characterized members have been shown to possess ATP-binding and hydrolysing activities as well as ATP-dependent RNA helicase activities. Most of the genes encoding such proteins have been isolated from yeast, on which we will focus in this review. From sequence data, three of the members form a subfamily, the D-E-A-H subfamily.

Analysis of a murine male germ cell-specific transcript that encodes a putative zinc finger protein

A cDNA species, corresponding to a gene with testis-specific expression (TSGA), was isolated from a testis cDNA library. The temporal and spatial expression of TSGA was studied by in situ hybridization as well as RNA filter hybridization. In tissue sections, the TSGA sequence was confined to cells within the seminiferous tubules. For filter hybridization, RNA was isolated from testis of prepubertal rats of different ages as well as from enriched populations of various germ cell types. It was found that TSGA is expressed only in male germ cells and that the steady-state level of TSGA transcripts reaches a maximum during the meiotic and the postmeiotic stages of germ cell development, suggesting a meiotic or postmeiotic function for the encoded protein. TSGA encodes a putative protein having 1,214 amino acids and contains a zinc finger, a structure that previously has been shown to mediate binding to nucleic acids.

Divergent genes for translation initiation factor eIF-4A are coordinately expressed in tobacco

Three cDNA clones coding for eukaryotic translation initiation factor 4A, eIF-4A, were isolated from a Nicotiana plumbaginifolia root cDNA library by heterologous screening. The clones comprise two distinct gene classes as two clones are highly similar while the third is divergent. The genes belong to a highly conserved gene family, the DEAD box supergene family, although the divergent clone contains a DESD box rather than the characteristic DEAD box. The two clones are representatives of separate small multigene families in both N. plumbaginifolia and N. tabacum. Representatives of each family are coordinately expressed in all plant organs examined. The 47 kD polypeptide product of one clone, overexpressed in E. coli, crossreacts immunologically with a rabbit reticulocyte eIF-4A polyclonal antibody. Taken together the data suggest that the two Nicotiana eIF-4A genes encode translation initiation factors. The sequence divergence and the coordinate expression of the two Nicotiana eIF-4A families provide an excellent system to determine if functionally distinct eIF-4A polypeptides are required for translation initiation in plants.

Translation initiation factor 4A from Saccharomyces cerevisiae: analysis of residues conserved in the D-E-A-D family of RNA helicases

The eukaryotic translation initiation factor 4A (eIF-4A) possesses an in vitro helicase activity that allows the unwinding of double-stranded RNA. This activity is dependent on ATP hydrolysis and the presence of another translation initiation factor, eIF-4B. These two initiation factors are thought to unwind mRNA secondary structures in preparation for ribosome binding and initiation of translation. To further characterize the function of eIF-4A in cellular translation and its interaction with other elements of the translation machinery, we have isolated mutations in the TIF1 and TIF2 genes encoding eIF-4A in Saccharomyces cerevisiae. We show that three highly conserved domains of the D-E-A-D protein family, encoding eIF-4A and other RNA helicases, are essential for protein function. Only in rare cases could we make a conservative substitution without affecting cell growth. The mutants show a clear correlation between their growth and in vivo translation rates. One mutation that results in a temperature-sensitive phenotype reveals an immediate decrease in translation activity following a shift to the nonpermissive temperature. These in vivo results confirm previous in vitro data demonstrating an absolute dependence of translation on the TIF1 and TIF2 gene products.

Translation initiation factor 4A from Saccharomyces cerevisiae: analysis of residues conserved in the D-E-A-D family of RNA helicases

The eukaryotic translation initiation factor 4A (eIF-4A) possesses an in vitro helicase activity that allows the unwinding of double-stranded RNA. This activity is dependent on ATP hydrolysis and the presence of another translation initiation factor, eIF-4B. These two initiation factors are thought to unwind mRNA secondary structures in preparation for ribosome binding and initiation of translation. To further characterize the function of eIF-4A in cellular translation and its interaction with other elements of the translation machinery, we have isolated mutations in the TIF1 and TIF2 genes encoding eIF-4A in Saccharomyces cerevisiae. We show that three highly conserved domains of the D-E-A-D protein family, encoding eIF-4A and other RNA helicases, are essential for protein function. Only in rare cases could we make a conservative substitution without affecting cell growth. The mutants show a clear correlation between their growth and in vivo translation rates. One mutation that results in a temperature-sensitive phenotype reveals an immediate decrease in translation activity following a shift to the nonpermissive temperature. These in vivo results confirm previous in vitro data demonstrating an absolute dependence of translation on the TIF1 and TIF2 gene products.

deaD, a new Escherichia coli gene encoding a presumed ATP-dependent RNA helicase, can suppress a mutation in rpsB, the gene encoding ribosomal protein S2

We have cloned and sequenced a new gene from Escherichia coli which encodes a 64-kDa protein. The inferred amino acid sequence of the protein shows remarkable similarity to eIF4A, a murine translation initiation factor that has an ATP-dependent RNA helicase activity and is a founding member of the D-E-A-D family of proteins (characterized by a conserved Asp-Glu-Ala-Asp motif). Our new gene, called deaD, was cloned as a gene dosage-dependent suppressor of temperature-sensitive mutations in rpsB, the gene encoding ribosomal protein S2. We suggest that the DeaD protein plays a hitherto unknown role in translation in E. coli.

A cold-sensitive mRNA splicing mutant is a member of the RNA helicase gene family

We have isolated a cold-sensitive mutant of Saccharomyces cerevisiae in which the first step of mRNA splicing is inhibited. The growth and splicing defects are recessive and cosegregate, thus defining a single essential gene (PRP28). The wild-type PRP28 gene was cloned, and sequence analysis reveals extensive homology to a family of proteins that are thought to function as ATP-dependent RNA helicases. The cold sensitivity is caused by a glycine-to-glutamic acid change in a conserved sequence motif. Interestingly, double mutants containing conditional alleles of PRP28 and PRP24, which encodes a U6 snRNA-binding protein, are inviable. In addition, a suppressor of prp28-1 is a mutant allele of PRP8, which encodes a U5 protein, thus linking PRP28 with U5. These data are consistent with a scenario in which PRP28 acts to unwind the U4/U6 base-pairing interaction in the U4/U6/U5 snRNP, facilitating the first covalent step of splicing.

A suppressor of yeast spp81/ded1 mutations encodes a very similar putative ATP-dependent RNA helicase

The spp81/ded1 mutations were isolated as suppressors of a Saccharomyces cerevisiae pre-mRNA splicing mutation, prp8-1. The SPP81/DED1 gene encodes a putative ATP-dependent RNA helicase. While attempting to clone the wild-type SPP81/DED1 gene we isolated plasmids which were able to suppress the cold-sensitive growth defect of spp81 mutants. These plasmids encoded a gene (named DBP1) which mapped to chromosome XVI and not to the SPP81/DED1 locus on chromosome XV. The cloned gene suppressed the defect of spp81/ded1 mutants when present on both high and low copy-number plasmids but complemented spp81/ded1 null mutants only when present on high copy-number plasmids. In contrast to the SPP81/DED1 gene the DBP1 gene was not essential for cell viability. The nucleotide sequence of the DBP1 gene revealed that it also encoded a putative ATP-dependent RNA helicase which showed considerable similarity at the amino acid level to the SPP81/DED1 protein.

Methylation patterns of testis-specific genes

The methylation patterns of genes expressed in the mouse male germ line have been examined. Int-1, Hox-2.1, and Prm-1, all of which contain 5' CpG islands, were found to be completely unmethylated at many sites in these domains, both in somatic tissues and in sperm DNA. Many other testis-specific genes have a similar structure and are probably also constitutively unmethylated. Pgk-2, a non-CpG-island gene, is similar to somatic tissue-specific genes in that it is highly methylated in nonexpressing cell types but undermethylated in pachytene spermatocytes and round spermatids, where it is actively transcribed. At later stages of spermatogenesis, however, the gene becomes remethylated and thus acquires the full modification pattern in sperm DNA. In all these cases, the sperm DNA that emerges from the testis does not contain any germ-line-specific unmethylated sites and thus carries the methylation pattern typical of that in somatic tissues.

A second maternally expressed Drosophila gene encodes a putative RNA helicase of the "DEAD box" family

Recently, a family of proteins containing the conserved motif Asp-Glu-Ala-Asp, the "DEAD box" proteins, has been identified. This family is typified by the eukaryotic translation initiation factor eIF4A, and its members are believed to share the functional property of ATP-dependent RNA unwinding. One of the previously identified members of this family (vasa) is the product of a maternally expressed gene from Drosophila melanogaster that is known to play a role in the formation of the embryonic body plan. We report here the isolation of a Drosophila gene that has an mRNA expression pattern somewhat similar to that of vasa and also encodes a DEAD box protein. We have termed this gene ME31B to reflect its maternal (ovarian germ-line) expression and its location within the 31B chromosome region. Comparisons with the other members of this family reveal that although ME31B is most like the protein Tif1/Tif2, which probably represents the Saccharomyces cerevisiae version of eIF4A, it is unlikely that ME31B represents the Drosophila eIF4A protein per se. A search for mutations in the ME31B gene has established that the P element which causes the female-sterile mutation flipper lies in the 3' flank of the ME31B gene.

Isolation and characterization of irradiation fusion hybrids from mouse chromosome 1 for mapping Rmc-1, a gene encoding a cellular receptor for MCF class murine retroviruses

An irradiation-reduced somatic cell hybrid mapping panel was constructed of BALB/c mouse Chromosome 1. Nineteen hybrids were selected from a pool of 292 clones to generate a fine structure physical map of the distal 40 cM of the chromosome. The hybrids contain mouse DNA fragments only from Chromosome 1, ranging from approximately 5 cM to approximately 20 cM. Utilizing a viral infectibility assay, a cellular receptor gene, Rmc-1, for the MCF class of murine retroviruses was found to be linked to Lamb2, in the region between the Lamb2 and Bxv-1 loci. In addition, analysis of the hybrid mapping panel resulted in the remapping of three loci, Atpb, Ly-5, and Pmv-24, as compared to the mouse linkage map. Two previously unmapped endogenous proviruses are also putatively assigned positions on the chromosome.

A suppressor of a yeast splicing mutation (prp8-1) encodes a putative ATP-dependent RNA helicase

Five small nuclear RNAs (snRNAs) are required for nuclear pre-messenger RNA splicing: U1, U2, U4, U5 and U6. The yeast U1 and U2 snRNAs base-pair to the 5' splice site and branch-point sequences of introns respectively. The role of the U5 and U4/U6 small nuclear ribonucleoprotein particles (snRNPs) in splicing is not clear, though a catalytic role for the U6 snRNA has been proposed. Less is known about yeast splicing factors, but the availability of genetic techniques in Saccharomyces cerevisiae has led to the identification of mutants deficient in nuclear pre-mRNA splicing (prp2-prp27). Several PRP genes have now been cloned and their protein products characterized. The PRP8 protein is a component of the U5 snRNP and associates with the U4/U6 snRNAs/snRNP to form a multi-snRNP particle believed to be important for spliceosome assembly. We have isolated extragenic suppressors of the prp8-1 mutation of S. cerevisiae and present here the preliminary characterization of one of these suppressors, spp81. The predicted amino-acid sequence of the SPP81 protein shows extensive similarity to a recently identified family of proteins thought to possess ATP-dependent RNA helicase activity. The possible role of this putative helicase in nuclear pre-mRNA splicing is discussed.

The Xenopus localized messenger RNA An3 may encode an ATP-dependent RNA helicase

The maternal messenger RNA An3 was originally identified localized to the animal hemisphere of Xenopus laevis oocytes, eggs and early embryos. Xenopus embryos depend on mRNA and protein present in the egg before fertilization (maternal molecules) to provide the information needed for early development. Localization of maternal mRNA gives cells derived from different regions of the egg distinctive capacities for protein synthesis. We show here that An3 mRNA encodes a protein with 74% identity to a protein encoded by the testes-specific mRNA PL10 found in mouse, which is proposed to have RNA helicase activity. Because the gene encoding An3 mRNA is reactivated after gastrulation and remains active throughout embryogenesis, we have examined its distribution in embryonic and adult tissues. Unlike PL10 mRNA, which is primarily restricted to the testes, An3 mRNA is broadly distributed in later development.

Translational potentiation of messenger RNA with secondary structure in Xenopus

Differential translation of messenger RNA (mRNA) with stable secondary structure in the 5' untranslated leader may contribute to the dramatic changes in protein synthetic patterns that occur during oogenesis and early development. Plasmids that contained the bacterial gene chloramphenicol acetyltransferase and which encoded mRNA with (hpCAT) or without (CAT) a stable hairpin secondary structure in the 5' noncoding region were transcribed in vitro, and the resulting mRNAs were injected into Xenopus oocytes, eggs, and early embryos. During early oogenesis, hpCAT mRNA was translated at less than 3 percent of the efficiency of CAT mRNA. The relative translational potential of hpCAT reached 100 percent in the newly fertilized egg and returned to approximately 3 percent after the midblastula transition.

A novel RNA helicase gene tightly linked to the Triplo-lethal locus of Drosophila

The Triplo-lethal (Tpl) locus of Drosophila is the only known locus which is lethal when present in three copies rather than the normal two. After recovering a hybrid-dysgenesis-induced mutation of Tpl we used a rapid combination of transposon tagging, chromosome microdissection and PCR to clone the P element that had transposed into the Tpl region. That P element is located within the gene for a new and unique member of the RNA helicase family. This new helicase differs from all others known by having glycine-rich repeats at both the amino and carboxyl termini. Curiously, genetic analysis shows that the P element inserted into this gene is not responsible for the Tpl mutant phenotype. We present possible explanations for these findings.

Translation initiation and ribosomal biogenesis: involvement of a putative rRNA helicase and RPL46

Cold-sensitive mutations in the SPB genes (spb1-spb7) of Saccharomyces cerevisiae suppress the inhibition of translation initiation resulting from deletion of the poly(A)-binding protein gene (PAB1). The SPB4 protein belongs to a family of adenosine triphosphate (ATP)-dependent RNA helicases. The aberrant production of 25S ribosomal RNA (rRNA) occurring in spb4-1 mutants or the deletion of SPB2 (RPL46) permits the deletion of PAB1. These data suggest that mutations affecting different steps of 60S subunit formation can allow PAB-independent translation, and they indicate that further characterization of the spb mutations could lend insight into the biogenesis of the ribosome.

Identification of five putative yeast RNA helicase genes

The RNA helicase gene family encodes a group of eight homologous proteins that share regions of sequence similarity. This group of evolutionarily conserved proteins presumably all utilize ATP (or some other nucleoside triphosphate) as an energy source for unwinding double-stranded RNA. Members of this family have been implicated in a variety of physiological functions in organisms ranging from Escherichia coli to human, such as translation initiation, mitochondrial mRNA splicing, ribosomal assembly, and germinal line cell differentiation. We have applied polymerase chain reaction technology to search for additional members of the RNA helicase family in the yeast Saccharomyces cerevisiae. Using degenerate oligonucleotide primers designed to amplify DNA fragments flanked by the highly conserved motifs V L D E A D and Y I H R I G, we have detected five putative RNA helicase genes. Northern and Southern blot analyses demonstrated that these genes are single copy and expressed in yeast. Several members of the RNA helicase family share sequence identity ranging from 49.2% to 67.2%, suggesting that they are functionally related. The discovery of such a multitude of putative RNA helicase genes in yeast suggests that RNA helicase activities are involved in a variety of fundamentally important biological processes.

A lysine substitution in the ATP-binding site of eucaryotic initiation factor 4A abrogates nucleotide-binding activity

Eucaryotic initiation factor 4A (eIF-4A) is a member of a family of proteins believed to be involved in the ATP-dependent melting of RNA secondary structure. These proteins contain a derivative of the consensus ATP-binding site AXXGXGKT. To assess the importance of the consensus amino acid sequence in eIF-4A for ATP binding, we mutated the consensus amino-proximal glycine and lysine to isoleucine and asparagine, respectively. The effect of the mutations was examined by UV-induced cross-linking of [alpha-32P]dATP to eIF-4A. Mutation of the lysine residue (but not of the glycine residue) resulted in the loss of [alpha-32P]dATP cross-linking to eIF-4A, suggesting that the lysine is an important determinant in ATP binding to eIF-4A.

A lysine substitution in the ATP-binding site of eucaryotic initiation factor 4A abrogates nucleotide-binding activity

Eucaryotic initiation factor 4A (eIF-4A) is a member of a family of proteins believed to be involved in the ATP-dependent melting of RNA secondary structure. These proteins contain a derivative of the consensus ATP-binding site AXXGXGKT. To assess the importance of the consensus amino acid sequence in eIF-4A for ATP binding, we mutated the consensus amino-proximal glycine and lysine to isoleucine and asparagine, respectively. The effect of the mutations was examined by UV-induced cross-linking of [alpha-32P]dATP to eIF-4A. Mutation of the lysine residue (but not of the glycine residue) resulted in the loss of [alpha-32P]dATP cross-linking to eIF-4A, suggesting that the lysine is an important determinant in ATP binding to eIF-4A.