Regulated expression of immunoglobulin trans-mRNA consisting of the variable region of a transgenic mu chain and constant regions of endogenous isotypes

Our previous work demonstrated that chimeric immunoglobulin mRNAs (trans-mRNAs) composed of a transgenic VHDJH region and endogenous CH sequences could be synthesized, most likely by a trans-splicing mechanism, in a transgenic line carrying a rearranged human membrane-type mu chain gene. In this study we further investigated regulation of trans-mRNA expression. Regulated expression of different gamma subclasses of trans-mRNA was similar to that of class switching: IL-4 together with lipopolysaccharide (LPS) predominantly increased the amount of gamma 1 trans-mRNA whereas LPS alone mainly induced gamma 3 and gamma 2b trans-mRNAs. Expression of the gamma class trans-mRNAs was preceded by germline transcription from the corresponding CH genes, but the co-existence of such germline transcripts and transgene transcripts was not sufficient for trans-mRNA production. Transforming growth factor-beta induced germline transcripts of the alpha chain CH gene but had no obvious effects on alpha trans-mRNA induction. Both C alpha gene alleles were used in trans-mRNA but in different frequencies. We could also detect trans-mRNA expression in another transgenic mouse line which carries a rearranged mouse VHDJH-C mu gene. These results indicate that trans-mRNA synthesis is not restricted to either a particular transgenic line or an isotype, but is a general mechanism to express a second isotype with the VH regions of rearranged mu chain transgenes.

Physical map of the 3′ region of the human immunoglobulin heavy chain locus: clustering of autoantibody-related variable segments in one haplotype

We have constructed the physical map of the 3' region of the human immunoglobulin heavy chain variable region (VH) genes. DNA segments extending to 200 kb upstream of the JH segment were isolated in two YAC clones. Five VH segments were identified in this region in the 5' to 3' order, V(II-5), V(IV-4), V(I-3), V(I-2), and V(VI-1) segments which were all structurally normal and orientated in the same direction as the JH segments. From DNA of a different cell line we have isolated a cosmid contig containing the same DNA region which has extraordinary polymorphism. The YAC and cosmid DNAs were called haplotypes A and B, respectively. Haplotype B contained an additional VH-I segment (V(I-4.1b)) between the V(II-5) and V(IV-4) segments. V(I-4.1b) segment is almost identical to a previously published VH sequence encoding a rheumatoid factor. Another VH segment in the B haplotype (V(I-3b)) corresponding to the V(I-3) segment also showed 99.7% nucleotide sequence homology with an anti-DNA autoantibody VH sequence. However, none of the VH sequences in haplotype A showed such strong homology with autoantibody VH sequences. The results suggest that VH haplotypes may have linkage with autoantibody production.

Expression of the RAG-2 gene in murine central nervous system tumor cell lines

Two tightly linked recombination activating genes, RAG-1 and RAG-2, are involved in VDJ recombination of the immune system. Although these genes were originally thought to be expressed exclusively in precursor B and T cells, RAG-1 transcripts were recently found in the murine central nervous system (CNS) [Chun et al., Cell 6, 189, (1991)]. We found that the RAG-2 gene was expressed in CNS tumor cell lines, melanoma (B-16) and skin fibroblast (A9). RAG-1 expression was not found in any non-lymphoid cell lines examined including CNS tumor cell lines. Another VDJ recombination-related gene RBP-Jk was expressed in all tumor cell lines examined. It remains to be seen whether expression of RAG-1 and RAG-2 in CNS is abortive or functionally important.

Biochemical evidence for a third chain of the interleukin-2 receptor

Two receptor proteins that specifically bind interleukin-2 (IL-2) have been identified previously. The L (Tac or alpha) chain can bind IL-2 with a Kd value of 10 nM (low affinity). Although the H (beta) chain expressed on lymphocytes can bind IL-2 with a Kd value of 1 nM (intermediate affinity), transfected fibroblasts expressing the H chain cannot bind IL-2, suggesting the involvement of other lymphocyte-specific factors for the function of the H chain. To obtain direct evidence for the presence of a third component of the IL-2 receptor, we examined the IL-2 binding activity of detergent-solubilized cell membrane preparations. We found that lysates of transfected Cos7 cells expressing H chains can bind IL-2 when mixed with lysates from lymphocytes that cannot bind IL-2. Chemical cross-linking of 125I-IL-2-bound lysate mixture and subsequent immunoprecipitation with a noncompetitive anti-H chain antibody gave rise to two 125I-IL-2-bound proteins, a 56-kDa protein (p56) and the H chain, although neither the H chain nor p56 alone is able to bind IL-2. These results indicate that p56 is the IL-2 receptor third chain that is required for IL-2 binding to the H chain. A similar lysate mixing experiment also showed that p56 is involved in IL-2 binding to the high affinity IL-2 receptor by forming the quaternary complex of IL-2, p56, L chain, and H chain.

Comparison of protein tyrosine phosphorylation and morphological changes induced by IL-2 and IL-3

We constructed cell lines which can proliferate in response to IL-2 or IL-3 by introducing a wild-type and mutant forms of cDNAs encoding the human IL-2R p75 chain into an IL-3 dependent hematopoietic cell line which expresses the p55 chain of the IL-2R. We compared early events that were induced in these cells by IL-2 and IL-3. Analysis of protein tyrosine phosphorylation showed that two common protein bands, pp95 and pp90, were phosphorylated by stimulation of either IL-2 or IL-3, suggesting the possible sharing of part of a signal transduction pathway between IL-2R and IL-3R. Comparison of protein tyrosine phosphorylation profiles induced by IL-2 and IL-3 among a variety of cell lines revealed that the pp90 band is the common tyrosine phosphorylation substrate in the cell lines examined, although the general tyrosine phosphorylation pattern differed in each cell line. Mutant p75 molecules incapable of inducing tyrosine phosphorylation could bind and internalize IL-2, but could not support cell growth. We also found that swift changes of cytoskeletal protein organization are one of the early events caused by signal transduction through either IL-2R and IL-3R. Reorganization of cytoskeletal proteins seems to be associated with protein phosphorylation, as a significant portion of pp90 was found in a detergent-soluble fraction in IL-2 or IL-3 treated cells.

Recombination of exogenous interleukin 2 receptor gene flanked by immunoglobulin recombination signal sequences in a pre-B cell line and transgenic mice

We have constructed a plasmid, pLTR100, which contains human interleukin 2 receptor light (IL-2R L) chain cDNA in the inverted orientation relative to the upstream SV40 promoter. The cDNA segment is flanked by the immunoglobulin gene recombination signal sequences so that the cDNA segment can invert and the human IL-2R L chain is subsequently expressed under the control of the SV40 promoter. A murine pre-B cell line, 38B9, transfected with pLTR100 began to express the human IL-2R L chain on the cell surface. The frequency of human IL-2R L chain positive cells increased almost linearly up to 50% for 60 days of culture after transfection. Southern blot analysis and sequencing of the DNA fragments at the recombination junction confirmed that the cDNA segment was inverted in a signal sequence-dependent manner by the variable-diversity-joining recombination process. Transgenic mice bearing the recombination substrate DNA similar to pLTR100 expressed the human IL-2 L chain in the spleen, thymus, and bone marrow, but not in the other tissues examined at the detectable level. Both IgM- and CD3-positive cells expressed the human IL-2R L chain, indicating that this artificial DNA can serve as a substrate for recombination both in B- and T-cells and that another DNA segment may be necessary to confer the cell-type specificity on the substrate DNA.

Duplicated variable region genes account for double isotype expression in a human leukemic B-cell line that gives rise to single isotype-expressing cells

The SSK41 cell is an immunoglobulin IgM+ human neoplastic B-cell line that switches to IgG+ cells (SSK gamma) spontaneously. We isolated a derivative of SSK41 (SSKWB) that expressed both IgM and IgG. Studies on the Ig heavy chain gene organization have shown that the SSKWB cell had two identical VDJ genes on the same chromosome; one linked to the C mu gene and the other to the C gamma 1 gene, both of which are transcribed to produce mu- and gamma-mRNAs with the same VDJ sequence. We also isolated the two switch variants derived from the SSKWB cell by cell sorter: 1G (IgG+) and 11M (IgM+). The 1G cells contained two populations; one had a similar genetic organization as SSK gamma and expressed only IgG1, and the other carried the same genetic organization as the SSKWB cell but produced aberrantly spliced mu-chain mRNA, in which the hydrophobic signal sequence exon is directly joined to the C mu exon. Te 11M cell deleted the VDJ-C gamma 1 segment of the SSKWB cell and expressed IgM. These results raise the interesting possibility of another mechanism for class switching.

Characterization of the enhancer region for germline transcription of the gamma 3 constant region gene of human immunoglobulin

A constant region gene (C) of the immunoglobulin heavy chain can be transcribed as germline transcripts from a promoter located upstream of a switch region. We have studied the structure and function of the human C gamma 3 promoter region. When the human IgM-producing cell line SSK41 is stimulated with interleukin 4 (IL-4) in the presence of phorbol myristate acetate (PMA) or Staphylococcus aureus Cowan I, expression of germline C gamma 3 transcripts was specifically augmented within 4 h. Upstream DNA fragments flanking the I gamma 3 exon were fused with a reporter gene and tested for IL-4-induced promoter/enhancer activity by transfection of SSK41 cells. The DNA fragment between 450 and 250 bp upstream of the transcription initiation site of the C gamma 3 gene was shown to be required for transcriptional up-regulation by PMA and IL-4. The upstream 514 bp fragment of the I gamma 3 flanking region was shown to contain an enhancer activity in response to PMA and IL-4.

Trans-splicing as a possible molecular mechanism for the multiple isotype expression of the immunoglobulin gene

We analyzed the molecular mechanism for the immunoglobulin (Ig) multiple isotype expression using a transgenic mouse (TG.SA) model system. Though most of the endogenous mu chain expression was excluded by the expression of the human rearranged mu transgene in the TG.SA mouse, a significant portion of splenic B lymphocytes could express the transgenic human IgM and endogenous mouse IgG simultaneously after stimulation with lipopolysaccharide and interleukin 4. The fluorescence-activated cell sorter-purified population of the human IgM+/mouse IgG+ cells expressed mRNA that consisted of properly spliced sequences of the transgenic VHDJH and the endogenous mouse C gamma genes (trans-mRNA), together with the transgenic human mu mRNA and germline transcripts of the mouse C gamma gene, without apparent rearrangement of the transgene. We also found that a lymphoma tumor, derived from the cross between the TG.SA mouse and another transgenic mouse carrying Ig H chain enhancer-driven c-myc oncogene, expressed about equal levels of the trans-mRNA and the transgenic mu mRNA without DNA rearrangement in either the transgene or the endogenous mouse switch region. These findings strongly support our previous proposal that the trans-splicing can account for the multiple isotype expression in this transgenic model and also suggest that novel molecular mechanism(s) might be involved in this reaction.

Premature expression of the macrophage colony-stimulating factor receptor on a multipotential stem cell line does not alter differentiation lineages controlled by stromal cells used for coculture

We are interested to know whether expression of a lineage-specific growth factor receptor is deterministic to lineage commitment during hematopoiesis. For this purpose, we introduced the human c-fms gene into the multipotential stem cell clone LyD9 and two myeloid progenitor clones, L-GM3 and L-G3, cells that differentiate in response to granulocyte/macrophage colony-stimulating factor (GM-CSF) and granulocyte (G)-CSF, respectively. Although LyD9 cells have differentiation potential to become macrophages, c-fms transfectants of LyD9 and L-GM3 cells did not differentiate in response to human macrophage (M)-CSF. However, c-fms transfectants of L-G3 cells differentiated to neutrophils in response to human M-CSF. These results indicate that the M-CSF receptor requires a specific signal transduction pathway to exert its differentiational and proliferative effects. Furthermore, the M-CSF receptor can convey a granulocyte-type differentiation signal possibly by cooperating with the G-CSF receptor signal transduction pathway. The c-fms-transfected LyD9 cells as well as the original LyD9 cells differentiated predominantly into GM-CSF- and G-CSF-responsive cells by coculturing with PA6 and ST2 stromal cells, respectively. The results indicate that differentiation lineage is not affected by premature expression of the M-CSF receptor. Instead, the stromal cell used for coculture apparently controls lineage-selective differentiation of the multi-potential stem cell line.

Germline transcripts of the immunoglobulin heavy-chain and T cell receptor genes in a murine hematopoietic stem cell line LyD9 and its derivative cell lines

We compared germline transcript levels of immunoglobulin heavy chain and T cell receptor (TcR) genes in a murine hematopoietic stem cell line, LyD9, and its derivative cell lines. LyD9 cells can be induced to differentiate into at least three lineages, namely, B lymphocyte, macrophage, and granulocyte lineages. Although C mu transcripts were found in stem cells to B lymphocytes, other myeloid-committed cells also expressed significant amounts of C mu transcripts. Germline TcR transcripts did not show good correlation with differentiation potential and stages of hematopoietic cells. During this search we identified a novel germline transcript containing the JH-C microliter sequence in LyD9 and some of its derivative cells. Expression of mRNAs for immunoglobulin- and TcR-associated molecules (lambda 5, MB1 and CD3 delta) was widespread except for lambda 5 mRNA. Among three mRNAs encoding putative recombinase proteins, RAG-1 and RAG-2 mRNAs were not expressed in any cell lines tested, while RBP-2 mRNA was expressed ubiquitously.

Genomic organization of IgH gene compared with the expression of Bcl-2 gene in t(14;18)-positive lymphoma

In three lymphoma cell lines carrying t(14;18), named FL-18, FL-218, and FL-318, the genomic organization of IgH gene was compared with the expression of bcl-2 gene; the t(14;18) of the FL-18 cells occurred downstream from the major breakpoint cluster region (mbr) of a bcl-2 gene, and that of the FL-218 and FL-318 cells within the mbr. The FL-318 expressed the normal-sized bcl-2 transcript of 8.5-kb mRNA having the noncoding region 3 to the mbr, which was found in the FL-18, and the FL-218 lacking the intact bcl-2 gene did not. This finding suggests that in t(14;18)-positive lymphoma having the breakpoint within the mbr, transcription of the nontranslocated bcl-2 allele is not necessarily silent. In addition, the FL-218 and FL-318 expressed aberrant bcl-2 transcripts and heterogenous IgH transcripts lacking the VH region, and the bcl-2 transcripts each comigrated with parts of the sterile IgH mRNAs. The FL-318, which did not exhibit switch recombination on either IgH allele, contained abundant amounts of l gamma mRNAs, a prerequisite for the recombination into the C gamma locus. One of the I-mRNA species comigrated with the aberrant bcl-2 transcript. The FL-18 and FL-218 lacking the I gamma mRNAs had completed switch recombination of both IgH alleles. This result raises a possibility that deregulated bcl-2 transcription caused by t(14;18) is capable of playing a role in class switch recombination of IgH gene.

Different stromal cell lines support lineage-selective differentiation of the multipotential bone marrow stem cell clone LyD9

An interleukin 3-dependent multipotential stem cell clone, LyD9, has been shown to generate mature B lymphocytes, macrophages, and neutrophils by coculture with primary bone marrow stromal cells. We report here that coculture with the cloned stromal cell lines PA6 and ST2 can support differentiation of LyD9 cells predominantly into granulocyte/macrophage colony-stimulating factor (GM-CSF)- and granulocyte (G)-CSF-responsive cells, respectively. However, these stromal cell lines were unable to support lymphopoiesis of LyD9 cells. The GM-CSF-dependent line, L-GM, which was derived from LyD9 cells cocultured with PA6 stromal cells, could differentiate into macrophages and granulocytes in the presence of GM-CSF. The L-GM line can further differentiate predominantly into neutrophils by coculture with ST2 stromal cells. The G-CSF-dependent line, L-G, which was derived from LyD9 cells cocultured with ST2 stromal cells, differentiated into neutrophils in response to G-CSF. Although the stromal cell-supported differentiation of LyD9 cells required the direct contact between LyD9 and stromal cells, a small fraction of LyD9 cells that were pretreated with 5-azacytidine could differentiate into neutrophils and macrophages without direct contact with stromal cells. These results indicate that different stromal cell lines support lineage-selective differentiation of the LyD9 stem cell and that 5-azacytidine treatment can bypass the requirement of direct contact with stromal cells, albeit with a lower frequency.

Differentiation of a human eosinophilic leukemia cell line (EoL-1) by a human T-cell leukemia cell line (HIL-3)-derived factor

Differentiation of a human eosinophilic leukemia cell line, EoL-1, induced by the culture supernatant of a human ATL cell line, HIL-3 (HIL-3 sup) was compared with differentiation induced by defined cytokines. HIL-3 sup induced EoL-1 cells to express eosinophilic granules and segmented nuclei after 6 to 9 days of incubation. HIL-3 sup also induced the expression of Fc epsilon receptor II (Fc epsilon RII/CD23) and an eosinophil differentiation antigen EO-1 mainly on eosinophilic granule (+) cells. Furthermore, HIL-3 sup induced EoL-1 cells to respond to an eosinophil chemotactic factor, platelet activating factor. HIL-3 cells express messenger RNA (mRNA) of interleukin-5 (IL-5), macrophage colony-stimulating factor (M-CSF), and IL-3 but not granulocyte CSF (G-CSF). Granulocyte-macrophage CSF (GM-CSF) and tumor necrosis factor-alpha (TNF-alpha) were detected in the HIL-3 sup. Recombinant IL-2 (rIL-2), rIL-3, rIL-4, rIL-5, rM-CSF, and rGM-CSF did not induce eosinophilic granules. rG-CSF induced a few eosinophilic granule (+) cells, and TNF-alpha, which did not induce eosinophilic granules by itself, enhanced the ability of G-CSF to induce them. However, G-CSF and TNF-alpha did not induce the expression of Fc epsilon RII and EO-1 antigen. Moreover, anti-G-CSF, anti-TNF-alpha, anti-GM-CSF, anti-IL-3, and anti-IL-5 antibodies did not suppress the effect of HIL-3 sup on the differentiation of EoL-1 cells. All the data suggest that HIL-3 sup contains an unidentified factor that induces differentiation of EoL-1 cells, and that EoL-1 cells and HIL-3 sup provide an important model for the examination of differentiation mechanisms and functions of eosinophils.

The nucleolar localisation signal of the HTLV-I protein p27rex is important for stabilisation of IL-2 receptor alpha subunit mRNA by p27rex

In this study we investigated the mechanism of stabilisation of IL-2 receptor alpha subunit mRNA by the HTLV-I protein p27rex. We tested the role of the nucleolar targetting signal in rex by introducing mutations. Three deletion mutants could not express rex protein in the nucleolus and although protein was still expressed in the nucleoplasm none of the mutants could stabilise IL-2R alpha mRNA. A substitution mutant could be expressed in the nucleolus and could also stabilise IL-2R alpha mRNA. The data show that the nucleolar targetting signal is crucial for stabilisation of IL-2R alpha mRNA by rex and raise the possibility that transport of mRNA from nucleus to cytoplasm can involve the nucleolus.

Differentiation of growth signal requirement of B lymphocyte precursor is directed by expression of immunoglobulin

During B cell differentiation, at least three stages can be defined in terms of their growth signal requirement by using two different growth signals, which are recombinant interleukin 7 (IL-7) and a stromal cell clone PA6 which does not produce IL-7; first a PA6 dependent stage, second a PA6 + IL-7 dependent stage and third an IL-7 dependent stage. In order to test the possibility that this differentiation of growth signal requirement is controlled by the expression of functional immunoglobulin molecules, we have investigated the frequencies of PA6 + IL-7 dependent and IL-7 dependent cells which are present in the bone marrow of either mu-chain or kappa-chain gene transgenic mice. In a mu-chain gene transgenic mouse, the frequency of PA6 + IL-7 dependent cells is selectively reduced, while that of IL-7 dependent cells is selectively reduced in a kappa-chain gene transgenic mouse. This result suggests that expression of a functional mu-chain gene drives PA6 + IL-7 dependent cells to differentiate into the subsequent IL-7 dependent stage. Likewise, when mu-chain positive IL-7 dependent cells express a functional light-chain gene, their growth signal requirement changes into an IL-7 unreactive stage.

The membrane exons of the pseudo-gamma-chain gene of the human immunoglobulin are apparently functional and highly homologous to those of the gamma 1 gene

Nucleotide sequences of the membrane exons of human immunoglobulin pseudo-gamma gene and gamma 1 chain cDNA were determined and compared. The sequences of the membrane exons of the pseudo-gamma gene had no defective mutations in the coding regions or the exon-intron boundaries. The translated amino acid sequence was highly homologous to that of the active gamma 1 gene, with only one substitution, at the 16th amino acid of the M2 exon (valine/isoleucine). Our findings together with previous data strongly support the idea that the absence of product of the pseudo gamma gene is attributable to deletion of 5' flanking regions responsible for class switch recombination (S region) and transcription of the germline CH gene (I region). The S and I regions are, therefore, likely to be indispensable for the expression of the immunoglobulin gamma, epsilon and alpha genes.

Cloning and characterization of a protein binding to the J kappa recombination signal sequence of immunoglobulin genes

A protein with molecular weight of 60,000 that binds to the recombination signal sequence (RS) of the immunoglobulin J kappa segment was purified from the nuclear extract of a murine pre B cell line 38B9. This binding protein was found in lymphoid cell lines but not in non-lymphoid cell lines. The Kd value of the J kappa RS binding protein to the J kappa RS was 1 nM. The cDNA clone (RBP-2) was isolated based on partial amino-acid sequence of this protein. This cDNA encodes 526 amino-acid residues, and its sequence does not show extensive overall homology with any known proteins, but displays an interesting homology to a 40-residue region that is conserved among a subset of site specific recombinase (integrase family).

HTLV-1 p27rex stabilizes human interleukin-2 receptor alpha chain mRNA

Expression of the pX gene products (p40tax, p27rex and p21X-III) of human T cell leukemia virus type 1 (HTLV-1), which is known to be a causative agent of adult T cell lymphoma/leukemia, induces expression of the interleukin-2 receptor alpha chain (IL-2R alpha) on infected T cells. Comparison of IL-2R alpha promoter activities has revealed that the transcriptional activation of the promoter alone cannot explain the large numbers of IL-2R alpha expressed on HTLV-1 infected cells. We found that the rates of the IL-2R alpha mRNA degradation were greatly reduced in pX-positive cells as compared with pX-negative cells. Simultaneous transfection of the expression vector plasmid containing IL-2R alpha cDNA and similar plasmids containing various pX sequences showed that p27rex elongated the half life of IL-2R alpha mRNA. As p27rex did not affect the transport of the IL-2R alpha mRNA from nucleus to cytoplasm, prolongation of the IL-2R alpha mRNA half life by p27rex is ascribed to stabilization of the mRNA. Experiments using deletion mutants and chimeric constructs of the IL-2R alpha cDNA demonstrated that the coding sequence but not the 5' or 3' untranslated region of the IL-2R alpha mRNA sequence is responsible for its protection by p27rex.

Control of IL-2 receptor-alpha expression by IL-1, tumor necrosis factor, and IL-2. Complex regulation via elements in the 5' flanking region

We have analyzed the mechanisms by which IL-1, IL-2, and TNF regulate expression of IL-2R alpha chain in a rodent T cell line. All three cytokines induce detectable IL-2R alpha mRNA by themselves, but there is strong synergy between IL-1 or TNF, on the one hand, and IL-2, on the other. The earliest phase of induction by IL-1 is independent of protein synthesis. IL-1, but not TNF, also stimulates transient secretion of IL-2. This leads to an autocrine stimulation of a further increase in IL-2R alpha mRNA levels. When IL-2 secretion has dropped off, continued IL-2R alpha expression requires both IL-2 and IL-1. Most or all of this regulation is due to changes in the rate of transcription of the IL-2R alpha gene. The response to IL-1 and IL-2 depends on a segment in the IL-2R alpha 5' flanking region, upstream of all cis-acting regulatory elements previously identified in the human gene.

Control of IL-2 receptor-alpha expression by IL-1, tumor necrosis factor, and IL-2. Complex regulation via elements in the 5' flanking region

We have analyzed the mechanisms by which IL-1, IL-2, and TNF regulate expression of IL-2R alpha chain in a rodent T cell line. All three cytokines induce detectable IL-2R alpha mRNA by themselves, but there is strong synergy between IL-1 or TNF, on the one hand, and IL-2, on the other. The earliest phase of induction by IL-1 is independent of protein synthesis. IL-1, but not TNF, also stimulates transient secretion of IL-2. This leads to an autocrine stimulation of a further increase in IL-2R alpha mRNA levels. When IL-2 secretion has dropped off, continued IL-2R alpha expression requires both IL-2 and IL-1. Most or all of this regulation is due to changes in the rate of transcription of the IL-2R alpha gene. The response to IL-1 and IL-2 depends on a segment in the IL-2R alpha 5' flanking region, upstream of all cis-acting regulatory elements previously identified in the human gene.

Deletion of human JK segments by site-specific recombination recognizing the conserved nonamer and heptamer sequences

Mapping and partial sequencing of the productive K chain genomic DNA of FK-001 demonstrated a 1.8-kb deletion including the JK2, JK3, JK4, and JK5 segments. This deletion occurred between the heptamer recombination signal sequence of the JK2 segment and the heptamer-like sequence located 1.8 kb downstream of the JK2 segment. The recombination reaction kept the reciprocally joined signal sequences on the chromosome and deleted the intervening DNA segment. The cloned FK-001 K chain gene was expressed efficiently in mouse myeloma cells, demonstrating that the 1.8-kb deleted region conferred no functions for gene expression.