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, and the Warren Triennial Prize (shared with 
Thomas Cech). 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 re- 
versed, and clinical studies provide information 
or materials that help to unravel basic biological 
processes. An example of this is our use of sera 
from human patients to determine the roles of 
previously mysterious small particles in normal 
cells. 
Particles called small nuclear ribonucleopro- 
teins (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 roles in cells. 
Systemic lupus erythematosus (SEE) is one of a 
number of diseases in which an individual's im- 
mune system mistakenly makes antibodies against 
the body's own molecules. Curiously, molecules 
that are very abundant in cells and highly con- 
served, such as DNA, are the most common tar- 
gets of autoimmunity. Thus SEE patients often 
make autoantibodies against snRNPs. 
Using SEE patients' antibodies to probe both 
the structures and functions of snRNPs, we have 
investigated the roles of a number of different 
kinds of snRNPs in gene expression. These inves- 
tigations 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 splicing, an early step in gene 
expression. For a gene's product to be made, the 
information in the gene's DNA is transcribed into 
an RNA copy (called pre-mRNA) that, after being 
"processed," directs the synthesis of a protein 
product. The DNA and the pre-mRNA contain seg- 
ments called exons, which code for the gene's 
product, and segments called introns, which are 
noncoding regions interspersed between the 
exons. Before leaving the cell nucleus as mRNA, 
the pre-mRNA is cut, the exons are spliced back 
together, and the introns are discarded. The indi- 
vidual exons must be joined precisely and in the 
same order they originally occupied in the gene. 
Sometimes differences in the way exons are 
spliced can lead to different protein products in 
different tissues. 
Evidence that snRNPs play central roles in pre- 
mRNA splicing has been obtained in several types 
of experiments, including use of autoantibodies 
from SEE 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 
act to recognize the splice junctions and the so- 
called intron branch point (where an unusual 
RNA structure is formed as an intermediate in 
splicing) and then assemble together to align the 
exon ends so that precise splicing can occur. In 
this sense, snRNPs are much like ribosomal sub- 
units (which also contain both RNA and protein) 
that assemble 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, particularly during the 
first step of intron removal. Here, we have inves- 
tigated a bizarre type of splicing where exons 
from two separate gene transcripts are joined 
(trans-splicing) and have learned that trans-splic- 
ing does not require the Ul snRNP, because one 
of the transcripts contains intrinsic information 
that substitutes for Ul . Investigation of the mini- 
mal sequences and/or structures needed will fur- 
ther elucidate the role of snRNPs in the spliceo- 
some. The possibility that the most abundant 
nuclear RNP currently of unknown function, 
which contains 7SK RNA, may serve to recycle 
snRNPs after splicing is completed is likewise be- 
ing actively pursued. 
Mammalian cells also contain many minor 
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