A VARIANT OF THE ALPHA(2) SUBUNIT OF SOLUBLE GUANYLYL CYCLASE CONTAINS AN INSERT HOMOLOGOUS TO A REGION WITHIN ADENYLYL CYCLASES AND FUNCTIONS AS A DOMINANT-NEGATIVE PROTEIN

A variant of the alpha(2) subunit of soluble guanylyl cyclase (alpha(2i)) containing 31 additional amino acids was identified in a number of cell lines and tissues. The in-frame sequence of the insert was within the proposed catalytic domain of guanylyl cyclases and was homologous to a region within the putative catalytic domain of adenylyl cyclases. Messenger RNA for the new variant was detected in some but not all cell lines and tissues expressing the alpha(2) subunit, The novel form, as well as the alpha(2) subunit lacking the insert, were coexpressed with the beta(1) subunit in Sf9 and COS-7 cells; alpha(2)/beta(1), coexpression yielded a NO-sensitive recombinant protein, whereas the coexpressed alpha(2i)/beta(1) subunits exhibited no guanylyl or adenylyl cyclase activities. Because both subunits (alpha(2i)/ beta(1)) copurified, the novel variant retains its ability to heterodimerize. In coexpression experiments, the alpha(2i) subunit competed with the alpha(2) subunit for dimerization with the beta(1) subunit, thereby reducing alpha(2)/beta(1)-catalyzed guanylyl cyclase activity. These data show that the novel variant functions as a dominant negative protein and that post-transcriptional mRNA processing represents a potential mechanism for regulation of NO-sensitive guanylyl cyclase acitivity.