Site-specific base substitution and deletion mutations that enhance or suppress transcription of the SV40 major late RNA.

Transcriptional analysis of SV40 late promoter mutants indicates that the DNA sequence 5'-GGTACCTAACC-3' (map positions 294-304) is important in the control of SV40 late RNA expression. C to T base substitutions at map positions 298, 299 and 304 increased initiation of late RNA synthesis at map position 325 five to ten fold. G to A base substitutions at map positions 294 and 295 decreased RNA initiation by a factor of 2 to 3. Deletion of nucleotides 295-298 reduced RNA initiation by a factor of 4 to 5. S1 analysis of in vivo RNA, isolated 24-36 hr after infection, demonstrated that the four base deletion not only decreased RNA initiation at nucleotide 325, but also increased RNA initiation at three alternate sites located approximately 125 nucleotides upstream from the major late RNA initiation site.