Localization ofActive Promoters forEucaryotic RNA Polymerase II intheLongTerminal Repeat ofAvianSarcoma VirusDNA

Thenucleotide sequencesinthelongterminal repeatofavian sarcoma virus that arerecognized invitro byHeLacell RNA polymerase IIhavebeenidentified. Forthis purpose,various 5'and3'deletions were introduced into a cloned long terminal repeat fragment. Theeffects ofthese deletions on transcription initiation inHeLawhole-cell extracts were thenstudied. Threespecific transcripts have beenidentified. Themajortranscript isinitiated atnucleotide +1(relative tothe capsite). Deletion oftheupstream sequencebetween -299and-55hasno effect on thelevel oftranscription fromthis start site, whereas deletion ofthesequence downstream of-14drastically reduces thelevels oftranscription. Incontrast, deletion ofthesequencedownstream fromtheTATA boxhasno effect on the initiation or efficiency ofsynthesis ofthetwominorRNA species, whichare initiated ataround nucleotides -260and-105.Thetranscription ofthese RNA products, however, isabolished byanupstreamdeletion between -299and-55. Theseresults suggest that HeLacell RNA polymerase IIrecognizes invitro more than one promotersite presentinthelongterminal repeatoftheavian sarcoma virus genome anddefines thesequencesrequired forinitiation ofthemajor transcript. Uponinfection ofsensitive cells byretroviruses, thegenomic RNA isconverted intoa duplex DNA whichiseventually integrated into thehostchromosomal DNA (2). Intheprocess ofthis conversion oftheRNA,twolong terminalrepeats (LTRs) of350basepairs (bp), with nucleotide sequences derived fromthe5'aswell asthe3'endsoftheRNAgenome, aregenerated