CHLORELLA VIRUSES ENCODE MULTIPLE DNA METHYLTRANSFERASES

The > 320 kb dsDNA genomes of 16 viruses which infect Chlorella strain NC64A and 5 viruses infecting Chlorella strain Pbi were tested for th eir sensitivity/resistance to more than 80 DNA restriction endonucleas es. From the known methylation sensitivities of these enzymes to site- specific 5-methylcytosine and N-6-methyladenine DNA modifications, we deduce that the 16 NC64A viruses encode at least 13 different sequence -specific DNA methyltransferases and the 5 Pbi viruses encode at least 7 sequence-specific DNA methyltransferases. Each DNA methyltransferas e has a 2 to 4 base pair DNA recognition sequence. Some individual vir uses encode as many as ten different DNA methyltransferases, making th ese chlorella virus genomes among the most concentrated sources of DNA methyltransferase genes known.