Research in our laboratory is focused on controls
of gene expression at steps after initiation of transcription,
which are increasingly recognized as important means
of regulation. We are using biochemical and genetic
techniques to define the RNA-RNA and RNA-protein interactions
that mediate such regulation. At present, we are particularly
interested in a set of genes which are encoded by
polycistronic mRNAs but expressed at markedly different
levels from the same mRNA molecule.
One area explores strategies of translational control.
Experiments are in progress to demonstrate the mechanism
of translational coupling between two of the genes
and to determine more generally how coupling is used
either to coordinate expression of two adjacent genes
or to downregulate expression from one to the next.
In a new line of inquiry, we are exploring the principles
that govern the relative levels at which in-frame
overlapping genes are translated from the polycistronic
mRNAs. We are also initiating analysis of an extraordinarily
efficient translational start site which appears to
be enhancer-driven and hence has the potential to
reveal previously unrecognized interactions between
mRNA and the ribosome.
The second area of interest concerns polyadenylation
and processing of the mRNAs. The principal processing
enzyme is RNase E, the first endoribonuclease shown
to have a global role in mRNA stability and one that
resides in a large macromolecular complex called the
degradosome. Through study of strains deficient in
poly(A) polymerase and/or RNase E, the pathways the
mRNAs follow from their initial synthesis, processing,
to their ultimate decay have emerged. We also have
obtained evidence that the normal processing pathway
has several biological functions. By setting the steady
state levels of the mRNAs, it sets the appropriate
ratio of two essential DNA replication proteins made
from the overlapping genes. Later, it provides longer-lived
mRNA templates for proteins needed in large amounts,
and delays inactivation of the coding region for the
most abundant protein. Students and postdoctoral fellows
have always been the key contributors to all aspects
of our research program.
