The Mycobacterium avium-intracellulare complex dnaB locus and protein intein splicing

Intein is a protein sequence mebedded in-frame within a precursor protein a nd is posttranslationally excised by a self-catalytic protein splicing proc ess. Protein splicing is believed to follow a pathway requiring Cys, Ser, o r Thr residues at the intein N-terminus and substitutions other than Cys, S er, or Thr residues prevent splicing. We show that the dnaB locus in some s trains of M. avium-intracellulare complex (MAC) contains intein and that th e intein N-terminal amino acid is Ala [Ala-type]. We demonstrate that the M . avium DnaB precursor protein undergoes posttranslational proteolytic proc essing producing proteins corresponding to the sizes of the DnaB and intein . Further, by Western analysis we detect a protein corresponding to the siz e of the spliced DnaB protein in MAC cell extracts. Together, these results indicate that the Ala-type MAC DnaB inteins can splice and provide another example that points to an interesting alternative splicing mechanism (Sout h worth, M. W., Benner, J., and Perler, F. B., EMBO J. 19, 5019-5026, 2000) . (C) 2001 Academic Press.