Abstract
A 90-base-pair tract of a simple sequence composed of alternating guanosine and thymidine nucleotide residues (poly[d(GT) . d(CA)]) was inserted into the simian virus 40 genome at nucleotide 2666 (0.17 map units). The poly[d(GT) . d(CA)] insertion was stably maintained in the viral genome, but the variant virus grew more slowly than simian virus 40.