Arrangement of late RNAs transcribed from a 7.1-kilobase EcoRI vaccinia virus DNA fragment.

Three late transcripts have been mapped to the vaccinia virus 7.1-kilobase (kb) EcoRI F fragment, which is located approximately 85 kb from the left end of the viral genome. Hybrid selection and translation of RNA have demonstrated that these mRNAs encode three polypeptides with apparent molecular weights of 32,000 (32K), 26K, and 19K. The transcripts encoding the 32K and 19K polypeptides are synthesized in a leftward direction and overlap each other as well as the RNA encoding the early 110K polypeptide. In addition, the RNA encoding the 32K polypeptide also overlaps an early transcript of 1.35 kb (see accompanying paper). The transcript encoding the 26K polypeptide overlaps the early 2.45-, 0.6- to 0.7-, and 1.7-kb RNAs, and all four mRNAs are transcribed from left to right. The protein coding sequences for the 26K and 32K polypeptides lie outside the 7.1-kb DNA fragment. Due to their heterogeneity in size, each of the three late transcripts is undetectable as a distinct size by filter hybridization. In addition, although S1 mapping has detected the 5' terminus of the late RNA which maps entirely within this fragment, it has been unable to size and locate the 3' ends of all three transcripts, and this result indicates that the heterodisperse size of the RNAs is due to heterogeneity at the 3' ends of these transcripts. The cause of this heterogeneity in termination of transcription is not known.