CLONING AND SEQUENCE-ANALYSIS OF A SIGNAL PEPTIDASE-I FROM THE THERMOPHILIC CYANOBACTERIUM PHORMIDIUM-LAMINOSUM

Type I signal peptidases are a widespread family of enzymes which remo ve the presequences from proteins translocated across cell membranes, including thylakoid and cytoplasmic membranes of cyanobacteria and thy lakoid membranes of chloroplasts. We have cloned and sequenced a signa l peptidase gene from the thermophilic cyanobacterium Phormidium lamin osum which is believed to encode an enzyme common to both membrane sys tems. The deduced amino acid sequence is 203 residues long and althoug h the overall similarity among signal peptidases is rather low there a re a number of identifiable conserved regions present. The P. laminosu m enzyme is predicted to have a single transmembrane domain, in contra st to other Gram-negative bacterial sequences, but similar to other ty pe I signal peptidases.