Projects:

The SmpB-tmRNA pathway is comprised of SmpB and tmRNA which form a ribonucleotide complex that is involved in the 3 tagging of proteins, directing the tagged protein for proteolysis by intracellular proteases. The detailed investigation of the SmpB-tmRNA pathway is of importance given that tmRNA plays a known role in both symbiosis and pathogenesis. Conventionally, tmRNA functions during translation to alleviate the occurrence of ribosomes stalled on transcripts. However, tmRNA also has a regulatory role in several bacteria. My projects in the lab address aspects of the SmpB-tmRNA pathway that have received little, if any, attention. My first aim is to examine potential determinants required for tmRNA tagging. A short DNA sequence that is common to 99% of known tmRNA substrates in Caulobacter crescentus was identified in previous studies. Mutations will be made in this consensus motif and the effects of the mutation on tmRNA tagging will be examined. These studies will help define the tmRNA tagging determinants and provide insight into whether tagging is directed by such a DNA consensus motif or if tmRNA tagging also requires other contextual signals. Another aim investigates SmpB-tmRNA pathway regulation through studies of SmpB, a known co-factor of the SmpB-tmRNA pathway. Currently, the only known function of SmpB is in the SmpB-tmRNA pathway. SmpB binds tmRNA and protects it from degradation in C. crescentus, thereby regulating tmRNA activity. However, an understanding of SmpB regulation is lacking. An investigation of the expression of smpB during a single cell-cycle and the identification of the protease responsible for SmpB turnover will be determined. Ultimately, these results will help define the overall regulation of the SmpB-tmRNA pathway by determining the regulation of SmpB itself. Further, the identity of proteins and/or RNAs that interact with SmpB, and potentially the SmpB-tmRNA pathway, will be examined through both transposon mutagenesis and direct isolation. Through these studies, previously unidentified molecules that interact with SmpB will be found, and the influence of these factors on SmpB and the pathway can be determined.

Publications:

1. •Lessner FH et al. (2007) “Proteolytic adaptor for tmRNA-tagged proteins from α-proteobacteria.” J Bacteriol 189:272-5.
   

2. •Hong S-J, Lessner FH, Mahen EM, and Keiler KC (2007) “Proteomic identification of tmRNA substrates.” PNAS 104: 17128-33.