Transcriptional and translational mapping of a 6.6-kilobase-pair DNA fragment containing the junction of the terminal repetition and unique sequence at the left end of the vaccinia virus genome

Abstract

The penultimate EcoRI fragments from the left and right ends of the vaccinia virus genomes were cloned in phage lambda. Heteroduplex analysis and comparison of restriction fragments indicated that the inverted terminal repetition extended 780 base pairs (bp) beyond the EcoRI site or about 9,800 bp from each end of the genome. Detailed physical, transcriptional, and translational maps of the 6,600-bp left penultimate EcoRI fragment were prepared so as to extend previous maps of the 9,000-bp terminal EcoRI fragment. Polypeptides with molecular weights of 6,000 (6K polypeptide), 13,000, 19,000, 21,000, and 60,000 were synthesized in a reticulocyte cell-free system programmed with immediate early RNA (made in the presence of cycloheximide) or early RNA (made in the presence of cytosine arabinoside) and selected by hybridization to immobilized recombinant DNA. A 22K polypeptide was detected as a translation product of late RNA that hybridized to this DNA fragment. A variety of biochemical procedures were used to size and map the mRNA's. Of the five messages that hybridized to this 6,600-bp EcoRI fragment, only the one for the 21K polypeptide was encoded within the inverted terminal repetition and hybridized to the rightward-reading DNA strand. (Three additional early polypeptides were encoded within the first 9,000 bp of the inverted terminal repetition.) The remaining early polypeptides were encoded within the unique portion of the penultimate EcoRI fragment and were transcribed from the leftward-reading strand. Additional high-molecular-weight early RNAs of unknown function were also detected; however, there was no evidence indicating that mature mRNA's were spliced.