BACTERIAL REVERSE-TRANSCRIPTASE AND MSDNA

Retrons are a new class of genetic elements found in the chromosome of a large number of different bacteria. These elements code for a rever se transcriptase (RT) that is structurally similar to the polymerases of retroviruses. The retron associated RT is responsible for the produ ction of an unusual extrachromosomal satellite DNA, known as multicopy , single-stranded DNA (msDNA). Synthesis of msDNA is dependent on a no vel self-priming mechanism, resulting in the formation of a 2',5'-phos phodiester bond. A comparison of bacterial RTs is presented, noting co nserved and unique features of these polymerases. In addition, the ori gin, means of dissemination, and possible activities of these function ally obscure retroelements are discussed.