LexA/Signal peptidase superfamily

This signature is associated with serine peptidases belong to MEROPS peptidase families: S24 (LexA family, clan SF); S26A (signal peptidase I), S26B (signalase) and S26C TraF peptidase.

The S26 family includes Escherichia coli signal peptidase, SPase, which is a membrane-bound endopeptidase, with two N-terminal transmembrane segments and a C-terminal catalytic region [9823901]. SPase functions to release proteins that have been translocated into the inner membrane from the cell interior, by cleaving off their signal peptides.

The S24 family includes:

• the lambda repressor CI/C2 family and related bacterial prophage repressor proteins [10892750].
• LexA, the repressor of genes in the cellular SOS response to DNA damage [11551506].
• MucA and the related UmuD proteins, which are lesion-bypass DNA polymerases, induced in response to mitogenic DNA damage [8994967].
• RulA, a component of the rulAB locus that confers resistance to UV.

All of these proteins, with the possible exception of RulA, interact with RecA, which activates self cleavage either derepressing transcription in the case of CI and LexA [10692372] or activating the lesion-bypass polymerase in the case of UmuD and MucA. UmuD'2, is the homodimeric component of DNA pol V, which is produced from UmuD by RecA-facilitated self-cleavage. The first 24 N-terminal residues of UmuD are removed; UmuD'2 is a DNA lesion bypass polymerase [10692372, 11483531]. MucA [9925794, 11016960], like UmuD, is a plasmid encoded a DNA polymerase (pol RI) which is converted into the active lesion-bypass polymerase by a self-cleavage reaction involving RecA [11114935]

This group of proteins also contains proteins not recognised as peptidases as well as those classified as non-peptidase homologues as they either have been found experimentally to be without peptidase activity, or lack amino acid residues that are believed to be essential for catalytic activity.