Southern California Conferences for Undergraduate Research

Southern California Conferences for Undergraduate Research

Identification of the Amino Acid Sequence of the Mature PhrA Signaling Peptide of Streptococcus pneumoniae


Sharon Hoover, Amilcar Perez


Beth Lazazzera, Professor of Microbiology, Immunology, and Molecular Genetics Department, University of California Los Angeles

Quorum-sensing (QS) is the ability of bacterial cells to monitor population density and in return affect gene expression. The phrA/tprA cassette of Streptococcus pneumoniae (SP), a common human pathogen, resembles QS systems found in other Gram-positive bacteria. Consistent with this, TprA was previously found to be a negative regulator of phrA expression, and PhrA induced its own expression, presumably by antagonizing the activity of TprA. The PhrA protein is predicted to be secreted and cleaved to release a mature peptide from its C-terminal domain, which is then predicted to be imported into the cytoplasm to bind to TprA. Here we sought out to remove the C-terminal residues of phrA in order to confirm the identity of mature peptide. To determine this sequence, we create phrA alleles that express C-terminally truncated PhrA proteins. The truncation alleles of phrA were transformed into a SP strain that lacks the wild-type copy of phrA and contains a phrA-lacZ reporter. Expression levels of lacZ in cells containing either full-length or a truncated phrA allele were measured to determine the residues vital for the auto-inducing function of PhrA. Transformants containing any of the deletion constructs resulted in loss of phrA-lacZ expression, revealing that the C-terminal of PhrA possesses residues vital for mature-PhrA function. This study will aid in understanding the mechanism of gene expression controlled by PhrA and TprA and the role of these proteins in mediating a QS signal.

Presented by:

Amilcar Perez


Saturday, November 17, 2012




Broome Library

Presentation Type:

Poster Presentation