ORGANIZATION AND SEQUENCE OF THE SALI RESTRICTION-MODIFICATION SYSTEM

The organization and nucleotide (nt) sequences were determined for the genes encoding the SalI restriction and modification (R-M) system (recognition sequence 5'-GTCGAC-3') from streptomyces albus G. The system comprises two genes, salIR, coding for the restriction endonuclease (ENase, R.SalI; probably 315 amino acids (aa), a predicted M(r) of 35 305; product, G'TCGAC) and sal1M, coding for the methyltransferase (MTase, M.SalI; probably 587 aa, a predicted M(r) of 64943; product, GTCGm(6)AC). The genes are adjacent, they have the same orientation, and they occur in the order salIR then salIM. R.SalI contains a putative magnesium-binding motif similar to those at the active sites of R.EcoRI and R.EcoRV, but otherwise it bears little aa sequence similarity to other ENases. M SalI is a member of the m(6)A gamma class of MTases. In aa sequence it resembles M.AccI, another m(6)A gamma-MTase whose recognition sequence includes the SalI recognition sequence as a subset.