Effect of heat shock on DNA-dependent RNA polymerase from the cyanobacterium Synechococcus sp.

Purification of DNA-dependent RNA polymerase from exponentially growing cells of the cyanobacterium Synechococcus sp. is described in cultures grown at normal temperature (39 degrees C) and after heat shock (HS) (47 degrees C). Polyethyleneimine precipitation followed by chromatography and gel filtration steps results in a 39% yield. The enzyme has a component of molar mass of 43 kDa, designated sigma, in addition to the typical procaryotic beta' beta alpha 2 and gamma. The results suggest that Synechococcus RNA polymerase is similar to that of cyanobacterial and E. coli RNA polymerases. Electrophoresis of the HS preparation showed that the enzyme has a component of 18 kDa. This suggests the existence of a functional relationship between this protein and the HS response of Synechococcus RNA polymerase, probably in salvaging denatured RNA polymerase or helping to regain its native structure.