A synthetic rev gene containing substitutions which introduced unique restriction sites but did not alter the deduced amino acid sequence was used as a vehicle to construct mutations in rev. Insertion or substitution mutations within a domain of Rev resulted in proteins able to inhibit the function of Rev protein in trans. Rev function was monitored in a cell line, HLfB, which contained a rev- mutant provirus. HLfB cells require the presence of rev for virus production, which was conveniently monitored by immunoblot detection of p24gag. Trans-dominant mutants were identified after expression in bacteria and delivery into HLfB cells by protoplast fusion. In addition, the trans-dominant phenotype was verified by expression of the mutant proteins in HLfB cells after cotransfection. These studies define a region between amino acid residues 81 and 88 of rev, in which different mutations result in proteins capable of inhibiting Rev function.

Several aspects of Rous sarcoma virus gene expression, including transcription, translation, and protein processing, can occur within Escherichia coli containing cloned viral DNA. The viral long terminal repeat contains a bacterial promoter, and viral sequences at or near the authentic viral initiation codon permit the initiation of translation. These signals can direct the synthesis in E. coli of the viral gag gene precursor Pr76 or, when fused to a portion of the lacZ gene, a gag-beta-galactosidase fusion protein. Pr76 is processed into gag structural proteins in E. coli in a process which is dependent upon the gag product p15. These observations suggest that E. coli can be used for the introduction and analysis of mutations in sequences relevant to viral gene expression.

A highly polymorphic locus associated with the variable tandem repetition of a 35 bp consensus sequence was mapped to chromosome 10, band q26. Examination of leukocyte DNA from a cancer patient revealed the twenty-fold amplification of one allelic fragment of this locus, while the other allelic fragment demonstrated a normal copy number. In another patient, Southern blotting of leukocyte DNA detected the deletion of the 3'-flanking region from one tandem repeat allele. These results indicate that variable tandem repeats may mark highly unstable regions of DNA in the human genome which can be altered by changes more extensive than simple tandem repeat variation.