A TOPA INTEIN IN PYROCOCCUS-FURIOSUS AND ITS RELATEDNESS TO THE R-GYRINTEIN OF METHANOCOCCUS-JANNASCHII

A new intein coding sequence was found in a topA (DNA topoisomerase I) gene by cloning and sequencing this gene from the hyperthermophilic A rchaeon Pyrococcus furiosus. The predicted Pfu topA intein sequence is 373 amino acids long and located two residues away from the catalytic tyrosine of the topoisomerase. It contains putative intein sequence b locks (C, E, and H) associated with intein endonuclease activity, in a ddition to intein sequence blocks (A, B, F, and G) that are necessary for protein splicing. This DNA topoisomerase I intein is most related to a reverse gyrase intein from the methanogenic Archaeon Methanococcu s jannaschii. These two inteins share 31% amino acid sequence identity and, more importantly, have the same insertion sites in their respect ive host proteins. It is suggested that these two inteins are homologo us inteins present in structurally related, but functionally distinct, proteins, with implications on intein evolution and intein homing. (C ) 1998 Elsevier Science B.V.