A mutation which alters initiation of transcription by RNA polymerase III on the Ad5 chromosome.

Mutant dl 309 is a viable Ad5 deletion mutant. Whereas wild-type Ad5-infected HeLa cells contain two VAI RNA species [VAI(A) and VAI(G)] which differ by three nucleotides at their 5' ends, dl 309-infected HeLa cells contain VAI(G) but no VAI(A) RNA. Nucleotide sequence analysis indicates that dl 309 lacks two base pairs which precede the 5' end of VAI(A) by 22 nucleotides. Since the 5' ends of VAI RNAs are not processed, the 309 deletion serves to identify a portion of the sequence required for RNA polymerase III initiation. Since dl 309 grows as well as wild-type Ad5 in HeLa cells, the VAI(A) species is not essential for viral growth in these cells.