REPETITIVE SEQUENCES FOUND IN THE CHROMOSOME OF THE MYXOBACTERIUM NANNOCYSTIS EXEDENS ARE SIMILAR TO MSDNA - A POSSIBLE RETROTRANSPOSITION EVENT IN BACTERIA

The first reverse transcriptase (RT) to be found in a prokaryotic cell is encoded by an element called a retron which resides in the chromos ome of many different bacteria. In addition, all retrons code for a fu nctionally obscure RNA-DNA satellite molecule called msDNA. msDNA is s ynthesized from an RNA template by the retron-encoded RT. An unusual r etron element is described here from the myxobacterium Nannocystis exe dens. This retron does not appear to have a typical RT gene in close p roximity (1 kb) to the gene msd (which encodes the DNA strand of msDNA ). The gene msr (which encodes the RNA strand of msDNA) appears to be duplicated and flanks both sides of the msd gene. Also discovered thro ughout the chromosome of this bacterium is a set of repeated sequences related to msDNA. These repeat sequences match only part of the seque nce of msDNA and may have become incorporated into the chromosome of t his bacterium by reverse transcription.