Molecular Genetics ofRNA Processing and Behavior 
Michael Rosbash, Ph.D. — Investigator 
Dr. Rosbash is also Professor of Biology at Brandeis University and Adjunct Professor of Molecular Biology 
at Massachusetts General Hospital, Boston. He received his Ph.D. degree in biophysics from the Massa- 
chusetts Institute of Technology and was a postdoctoral fellow at the University of Edinburgh, where he 
studied with J. O. Bishop. Dr. Rosbash was a Guggenheim Fellow in Paris, France. 
MY laboratory is interested in two fundamen- 
tal problems. Our earliest and foremost in- 
terest is the molecular genetics of RNA process- 
ing. For this subject our principal experimental 
system is the budding yeast Saccharomyces cere- 
visiae, which is amenable to both genetic and 
biochemical attack. Our more recent interest is 
the molecular genetics of behavior — in particu- 
lar, circadian rhythms. This problem is addressed 
in the fruit fly Drosophila melanogaster, which 
is amenable to behavioral as well as biochemical 
and genetic approaches. 
A major objective in the field of RNA process- 
ing is to understand the rules that govern pre- 
mRNA splicing. It is now more than 10 years 
since splicing was discovered in mammalian cells 
and viruses. This discovery revolutionized the 
field of genetics, since it refuted a major tenet — 
that genes are intact units. It became clear that 
genes are divided into segments and that the inco- 
herent material (the introns) is discarded, while 
the retained sense material needed to code for 
proteins (the exons) is carefully sewn together. 
Neither the efficiency nor the specificity of the 
process is well understood. 
More recently it emerged that all eukaryotes 
(including S. cerevisiae) undergo the same splic- 
ing process with essentially the same biochemi- 
cal machinery. This includes a myriad of protein 
factors, most of which remain uncharacterized if 
not unidentified, and five small nuclear ribonu- 
cleoprotein particles (snRNPs) . Each snRNP con- 
tains one or two small molecules of RNA and per- 
haps 5-10 proteins. The pre-mRNA substrate and 
many of these factors, including the five snRNPs, 
assemble into the spliceosome, a large particle 
within which the cleavage and ligation events of 
splicing take place. 
We are particularly interested in the early 
events of the spliceosome assembly process, as it 
seems to be related to those of intron recognition 
or definition. The highly ordered assembly pro- 
cess must involve recognition of an appropriate 
pre-mRNA substrate to initiate the splicing pro- 
cess and prevent unproductive transport of the 
unspliced pre-mRNA to the cytoplasm. In addi- 
tion, these early events are likely related to the 
mysterious prevention of exon shuffling — i.e., 
exons are usually sewn together in the correct 
order. 
We have focused on Ul snRNP, as there was 
reason to believe that it features prominently in 
recognition of one of the two intron splice sites 
(the 5' splice site) and even in catalytic specific- 
ity. Our recent results indicate that Ul snRNP is 
indeed very important to the early stages of spli- 
ceosome assembly. Surprisingly, we found that it 
participates in the recognition of both splice 
sites, but that this recognition is not sufficient to 
define the specificity with which the splicing ma- 
chinery cleaves the 5' splice site. 
Genetics of Behavior 
The other aspect of our work is concerned with 
circadian rhythms. The choice of Drosophila was 
dictated by such factors as its suitability for ge- 
netic analysis and the large amount of behavioral 
work done on this animal. For example, it was 
known that its circadian rhythms, as in all other 
systems examined to date, manifest temperature 
compensation: i.e., the circadian rhythm periods 
(approximately 24 hours) change little if at all 
with temperature. 
The period {per) gene has a profound influ- 
ence on the animal's circadian rhythms. Alleles of 
the gene speed up, slow down, or apparently 
eliminate the animal's circadian rhythms. At least 
two different rhythms, including those of loco- 
motor activity (the animal's analogue of our 
sleep-wake cycle), are similarly affected. This 
work suggested that the per gene might consti- 
tute an entree into the mysterious world of the 
circadian oscillator. 
We have focused on the per gene and its prod- 
uct with the thought that it might code for a 
"clock molecule." This possibility is even 
stronger due to the characterization of a variety 
of mutant and transformed strains. 
Our experiments have reinforced the sugges- 
tion that the gene is making a physiological rather 
than developmental contribution to the oscilla- 
tor — i.e., it is carrying out a biochemical func- 
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