A novel DNA primase-helicase pair encoded by SCCmec elements.

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Mobile genetic elements (MGEs) are crucial sources of novel enzymes.
• Understanding MGE-encoded proteins aids in elucidating MGE functions.
• The Staphylococcal Cassette Chromosome (SCCmec) is an MGE conferring methicillin resistance in *Staphylococcus aureus* (MRSA).

Purpose of the Study:

• To biochemically characterize three proteins encoded by a conserved operon within SCCmec.
• To investigate the enzymatic activities and interactions of these SCCmec-encoded proteins.
• To determine if these proteins constitute a functional replication module for SCCmec.

Main Methods:

• Biochemical characterization of purified proteins.
• Enzyme activity assays (DNA polymerase, primase, helicase).
• Protein-protein interaction studies.

Main Results:

• CCPol was identified as an active A-family DNA polymerase.
• MP protein binds CCPol, enabling de novo DNA primer synthesis, forming a unique primase-polymerase complex.
• Cch2 functions as a 3'-to-5' helicase and binds a specific downstream dsDNA sequence, a preferred priming site for CCPol-MP.

Conclusions:

• The characterized CCPol-MP primase-polymerase and Cch2 helicase form a novel, functional replication module for SCCmec.
• This discovery provides insights into the replication mechanisms of MGEs.
• The findings contribute to understanding the biology of MRSA and SCCmec elements.