Autoantibody Probes for Mammalian 
Gene Expression 
Joan A. Steitz, Ph.D. — Investigator 
Dr. Steitz is also Professor of Molecular Biophysics and Biochemistry at Yale University School of Medicine. 
She received her Ph.D. degree in biochemistry and molecular biology ( with James Watson ) from Harvard 
University and did postdoctoral work at the Medical Research Council Laboratory of Molecular Biology 
(with Frances Crick) in Cambridge, England. Her many honors include the Passano Foundation Young 
Scientist Award, the Eli Lilly Award in Biological Chemistry, the U.S. Steel Award in Molecular Biology, 
the National Medal of Science, the Dickson Prize for Science, the Warren Triennial Prize (shared with 
Thomas Cech), and the Christopher Columbus Discovery Award. Dr. Steitz is a member of the National 
Academy of Sciences. 
KNOWLEDGE gained from basic research in 
the biomedical sciences sometimes pro- 
vides answers to key questions in clinical medi- 
cine. Occasionally, however, the path is reversed 
and clinical studies provide information or mate- 
rials that help to unravel basic biological pro- 
cesses. An example of this is our use of sera from 
human patients to determine the roles of previ- 
ously mysterious small particles in normal cells. 
Particles called small nuclear ribonucleoproteins 
(snRNPs: pronounced "snurps") are found in the 
nucleus of the cells of humans and other higher 
organisms. Each snRNP is a tight cluster of one or 
more proteins with a small RNA molecule. 
SnRNPs are abundant in virtually all human cells 
and are remarkably similar among various mam- 
malian species, suggesting that the particles must 
play important cellular roles. 
Systemic lupus erythematosus (SLE) is one of a 
number of diseases in which the immune system 
mistakenly makes antibodies against the body's 
own molecules. Curiously, molecules that are 
very abundant in cells and highly conserved in 
evolution, such as DNA, are the most common 
targets of autoimmunity. Thus SLE patients often 
make autoantibodies against snRNPs. 
Using SLE patients' antibodies to probe both 
the structures and functions of snRNPs, we have 
investigated the roles of various kinds of snRNPs 
in gene expression. These investigations began in 
1979 when studies by Michael Lerner (then an 
M.D./Ph.D. student; now HHMI, Yale University 
School of Medicine) led to the hypothesis that the 
most abundant snRNP in mammalian cells, called 
the Ul snRNP, might be involved in RNA splic- 
ing, an early step in gene expression. In the mak- 
ing of a gene's product, its information coded in 
DNA is transcribed into an RNA copy called pre- 
messenger RNA, which is then "processed" into 
mRNA to direct the synthesis of a protein. The 
DNA and the pre-mRNA contain segments called 
exons, which code for the gene's product, and 
segments called introns, which are intermittent 
noncoding regions. Before leaving the cell nu- 
cleus as mRNA, the pre-mRNA is cut, the exons 
are spliced together, and the introns discarded. 
The individual exons must be precisely joined in 
the order they originally had in the gene. Some- 
times differences in the way exons are spliced 
can lead to anomalous protein products in 
various tissues. 
Evidence that snRNPs play central roles in pre- 
mRNA splicing has been obtained in several types 
of experiments, including use of autoantibodies 
from SLE patients to inhibit splicing in active cell 
extracts. We now know that participation of the 
most abundant snRNPs in mammalian cells (the 
Ul , U2, U5, and U4/U6 particles) is essential and 
that splicing requires assistance from the snRNP 
proteins as well as their RNA molecules. SnRNPs 
recognize the splice junctions and the so-called 
intron branch point (where an unusual RNA 
structure is formed as an intermediate in splic- 
ing) and then assemble to align the exon ends so 
that precise splicing can occur. In this sense, 
snRNPs are much like the ribosomal subunits 
(also containing both RNA and protein) that as- 
semble onto an mRNA to translate it into protein. 
Current efforts in splicing are directed at un- 
derstanding exactly how RNA-RNA interactions in 
the active splicing body (called the spliceosome) 
contribute to catalysis. Here, we are using two 
types of crosslinking approaches to identify con- 
tacts between the pre-mRNA molecule and either 
proteins or snRNAs in the assembled splice- 
osome. Novel crosslinks are now being analyzed 
that suggest how a cut-off exon may be held in the 
spliceosome for subsequent ligation. Also evolv- 
ing is an increased understanding of how the 
spliceosome is related to some "self-splicing" in- 
trons, which are removed without proteins or 
other factors. 
Mammalian cells also contain many minor 
snRNPs that are closely related to the splicing 
snRNPs. One is the U7, which is only 1/1 ,000 as 
abundant as the splicing snRNPs. We have re- 
cently demonstrated that it participates in form- 
ing the 3' ends of histone mRNAs by using base- 
pairing to recognize a specific sequence in the 
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