The A+T-rich sequence of the simian virus 40 origin is essential for replication and is involved in bending of the viral DNA.

The origin-promoter region of simian virus 40 contains a 17-base-pair sequence composed exclusively of adenine (A) and thymine (T). We constructed a linker replacement mutant in which this stretch of A's and T's was reduced to 11 base pairs. While not affecting the level of early gene transcription, this mutation reduced the accumulation of viral DNA in COS cells at least 10(4) fold. In addition, a restriction fragment containing the wild-type A + T-rich region migrated in nondenaturing polyacrylamide gels with an anomalous mobility characteristic of bent DNA; however, the corresponding fragment from the mutant migrated less anomalously. Therefore, bending of the DNA in this region may play a role in some step in viral DNA replication.