We have cloned the REV3 gene of Saccharomyces cerevisiae by complementation of the rev3 defect in UV-induced mutagenesis. The nucleotide sequence of this gene encodes a predicted protein of Mr 172,956 showing significant sequence similarity to Epstein-Barr virus DNA polymerase and to other members of a class of DNA polymerases including human DNA polymerase a and yeast DNA polymerase I. REV3 protein shows less sequence identity, and presumably a more distant evolutionary relationship, to the latter two enzymes than they do to each other. Haploids carrying a complete deletion of REV3 are viable. We suggest that induced mutagenesis in S. cerevisiae depends on a specialized DNA polymerase that is not required for other replicative processes. REV3 is located 2.8 centimorgans from CDC60, on chromosome XVI.The REV3 gene of bakers' yeast, Saccharomyces cerevisiae, is concerned with a recovery process in which DNA damage causes mutations within the nuclear genome. It was identified by isolation of strains displaying reduced frequencies of UV mutagenesis (28), and, compared with others selected by such a criterion (25,26,28,32,37), strains carrying rev3 mutations exhibit one of the most extreme and general deficiencies in this respect. Relative to wild type, rev3 mutants display a 96% reduction in forward mutation to auxotrophy induced by UV (31) and also display defects in UV-induced reversion of broad range of base substitution and frameshift test alleles (24,27,28). The rev3 mutant is also deficient in mutagenesis by 4-nitroquinoline-1-oxide (41) and gamma rays (34), though response to ethyl methanesulfonate and nitrous acid is normal (31, 41). Spontaneous mutation is reduced to about one-fifth of normal in rev3 mutants, suggesting that the REV3-dependent recovery process may act on spontaneously arising damage (42). It does not, however, appear to be concerned with damage in the mitochondrial genome: UV-induced mutagenesis in mitochondrial DNA is normal in rev3 mutants (40, 45). These observations suggest that the REV3 gene product may function in translesion synthesis, that is in replication on mutagen-damaged templates, though they do not point to any specific role. The REV] gene (28), which has a mutant phenotype similar to that of REV3 and was identified in the same way, has recently been shown to encode a predicted protein of Mr 112,239 with sequence similarity to the Escherichia coli umuC gene (22). The umuDC genes of E. coli also have a mutant phenotype similar to that of REV3 and encode 16,000-and 45,000-Mr proteins that are thought to enhance the processivity of DNA polymerase (1,11

Two different cDNAs containing sequences coding for the beta-subunit of bovine follicle stimulating hormone (FSH-beta) have been isolated from a phage lambda gt11 bovine pituitary cDNA library. The complete nucleotide sequence of both clones was determined, and the combined sequence represents most of FSH-beta mRNA. The combined sequence contains 46 nucleotides of 5'-untranslated sequence followed by 387 nucleotides of coding sequence. The coding sequence predicts a 19-amino-acid amino-terminal precursor segment followed by the 110-amino-acid sequence of mature bovine FSH-beta. The cDNA sequence demonstrates the presence of a long 3'-untranslated region containing 1295 bases followed by a segment representing the poly(A) portion of the mRNA. Thus, the combined sequence of the cDNAs suggests a minimal size of 1.7 kb for FSH-beta mRNA. Analysis of FSH-beta sequences present in bovine pituitary mRNA demonstrated the presence of an mRNA with a size of about 2.0 kb. This apparent discrepancy is probably due to the presence of a several-hundred nucleotide tract of poly(A) at the 3' terminus of the mRNA. Comparison of the amino acid sequence predicted from the cDNA with the known amino acid sequence of the beta-subunit of FSH from several different species demonstrates that the protein has been highly conserved.

The chromosomal location of the human gene for erythropoietin (EPO) was determined by Southern blot hybridization analysis of a panel of human-mouse somatic hybrid cell DNAs. DNAs from cell hybrids containing reduced numbers of human chromosomes were treated with the restriction enzyme PstIand screened with a cloned human EPO cDNA probe. EPO is assigned to human chromosome 7 based on the complete cosegregation of EPO with this chromosome in all 45 cell hybrids tested. A cell hybrid containing a translocated derivative of chromosome 7 localizes EPO to 7pter→q22. A HindIII restriction fragment length polymorphism is detected by hybridization of the EPO cDNA probe to human genomic DNA.

A human genomic DNA fragment in phage lambda containing FSHB, the gene for the beta-subunit of human follicle-stimulating hormone (FSH-beta), was analyzed and the nucleotide sequence of the region of the clone encoding FSH-beta was determined. A subclone of the lambda phage containing 67% of FSH-beta coding sequence was used as hybridization probe to determine the human chromosomal location of FSHB. A panel of mouse-human somatic cell hybrids containing reduced numbers of human chromosomes was screened with the FSHB probe; complete cosegregation of FSHB with human chromosome 11 was observed in all 26 cell hybrids tested. Analysis of a set of cell hybrids containing translocated derivatives of chromosome 11 further localized FSHB to the human chromosome region 11p11.2----11pter. A Hind III restriction fragment length polymorphism (RFLP) detected by another subclone of the lambda phage containing FSHB now provides a genetic marker for this region of the human genome.

Partially purified protein preparations containing megakaryocyte growth factor activity were prepared from human embryonic kidney (HEK) cell conditioned medium using ammonium sulfate precipitation, Cibicron blue affinity chromatography, and wheatgerm lectin affinity chromatography. Treatment of these preparations with neutralizing antibodies directed against erythropoietin (EPO) and interleukin 6 (IL6) resulted in a dramatic reduction in their capacity to stimulate megakaryocyte maturation in vitro. The presence of EPO in these preparations was confirmed by both immunoblotting and use of a mouse spleen erythroid progenitor cell proliferation assay routinely used to quantitate EPO activity in vitro. Northern blot analysis of HEK cell-derived mRNA with IL6 DNA probes revealed the presence of an IL6 transcript with a molecular size of 1.3 kb. Analysis of the HEK cell-derived preparation by ELISA confirmed the presence of immunologically reactive IL6. In addition, it was shown that purified recombinant human EPO and IL6 stimulated megakaryocyte maturation in the in vitro assay used in this study. These data indicate that the activity in HEK cell conditioned medium that stimulates megakaryocyte maturation in vitro is predominantly due to the presence of IL6 and EPO. Immunoneutralization studies of another HEK cell-derived preparation, which was inhibitory in the megakaryocyte maturation assay, demonstrated that it contained transforming growth factor beta (TGF beta), a potent inhibitor of megakaryocyte maturation. Taken together, these studies indicate that HEK cell conditioned medium, which has previously been reported to contain megakaryocyte growth factor activity, is comprised of a complex mixture of growth and differentiation factors, some of which promote and others that inhibit the process of megakaryopoiesis.