Autoantibody Probes for Mammalian Gene Expression 
pre-mRNA just downstream of the cut site. Other 
related low- abundance snRNPs containing Ull 
and Ul 2 RNA interact to form a two-snRNP com- 
plex, but their function is unknown. 
A new autoantibody directed against the Ull 
snRNP has recently been found in the serum of a 
patient with scleroderma. Also in this group of 
-related snRNPs, which probably all function in 
some aspect of mRNA maturation, are viral 
snRNPs. For instance, in marmoset cells infected 
by Herpesvirus saimiri, which causes malignant 
transformation of the T cells, the viral genome 
encodes five small RNAs. Current results suggest 
that these viral snRNPs may act to slow the degra- 
dation of mRNAs coding for oncoproteins or 
growth factors, thereby enhancing the process of 
cellular transformation. 
Another type of patient autoantibody is di- 
rected against a different class of small RNPs lo- 
calized in the nucleolus, where ribosomal RNA 
processing and assembly occur. The most abun- 
dant nucleolar snRNP (containing U3 RNA) is es- 
sential for the first step of ribosomal RNA process- 
ing. Recent analyses have revealed how U3 binds 
to the ribosomal pre-RNA, making specific base 
pairs. Separate studies are dissecting the signals 
that dictate the delivery of the U3 and related 
snRNPs to their nucleolar site of action. 
Yet another autoantibody type precipitates 
EBERs, two small RNAs specified by Epstein-Barr 
virus (EBV), the causative agent of infectious 
mononucleosis, also implicated in several human 
cancers. Since EBERs are among the few viral 
products that are expressed in EBV-transformed 
cells, they must be important to the induction or 
maintenance of the transformed state. A highly 
abundant, highly conserved cell protein that 
binds the EBERs appears to reside in the cell's 
nucleolus. We hope that its further characteriza- 
tion will lead to an elucidation of EBER function. 
Thus autoantibodies are potent probes for de- 
ciphering some of the fundamental reactions oc- 
curring in all mammalian cells, those involved in 
gene expression. Characterization of new cellu- 
lar particles like snRNPs is significant for future 
studies of basic cellular processes and their alter- 
ation by disease. Furthermore, our research has 
provided new ways of diagnosing patient autoan- 
tibodies, which are helpful in the diagnosis and 
treatment of diseases like SLE. 
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