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Mammalian cells contain multiple copies of endogenous type C retroviral DNA sequences. Among these sequences are complete, potentially infectious proviruses, proviral DNA that is expressed only in the form of viral antigens, retroviral segments that may contribute portions of envelope (env) genes during the generation of recombinant polytropic viruses, and many subgenomic viral DNA segments that may not be expressed at all. We have previously reported the identification and molecular cloning of type C retroviral sequences from human DNA and have shown that the partial nucleotide and deduced amino acid sequences of one of the clones obtained (lambda 51) are homologous to Moloney MuLV (MoMuLV) in the gag and pol regions. The lambda 51 clone as well as several others isolated from a human DNA library contained approximately 4.3 kilobases (kb) of retroviral sequences, were deleted in the env region, and were flanked by tandem repeats unlike the long terminal repeats (LTRs) typically found in proviral DNAs (P.E.S., in preparation). We describe here the characterization of a full-length human retroviral clone (lambda 4-1) containing LTR elements as well as a putative env region. DNA-RNA hybridization experiments reveal that human cells contain species of poly(A)+ RNA that anneal to segments of the full-length retroviral DNA clone.

Vaccinia virus DNA contains a long inverted terminal repetition of MW approximately 6.8 x 10(6). A fragment of MW 6.3 X 10(6) from this repetition has been cloned in coliphage lambda and used to isolate RNA from virus-infected cells. Electron microscopy indicates that early RNAs are transcribed from the repeated sequence and cell-free translation shows that the RNAs code for polypeptides.

Epidemiological and immunological evidence indicates that the K1 capsular polysaccharide confers the property of virulence on Escherichia coli. E coli K1 is associated with invasive diseases in humans and in laboratory and domesticated animals. K1 isolates account for 80% of E. coli neonatal meningitis and comprise the majority of capsular types in neonatal septicaemia without meningitis and in childhood pyelonephritis. Passive administration of K1 antibodies prevented bacteraemia and meningitis in infant rats fed E. coli K1. Nonencapsulated derivatives of these invasive K1 strains did not cause bacteraemia in infant rats, although intestinal colonization was similar to that of the parent strains (M. Achtman and R.P.S., unpublished results). Several reports propose that the E. coli K1 capsular polysaccharide exerts an anti-phagocytic effect similar to that observed with other pathogenic encapsulated bacteria. One approach to studying whether the K1 antigen is sufficient to confer virulence of if other E. coli structures are necessary is to isolate the K1 genes for genetic and biochemical analysis. Recombinant DNA methodology provides a powerful tool for such an approach. Here, we report the molecular cloning of the E. coli K1 antigen genes. The cloned K1 genes synthesize a capsule in E. coli K12 indistinguishable chemically and immunologically from that of wild-type K1 strains.