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Molecular and Cellular Biology, January 1999, p. 376-383, Vol. 19, No. 1
Department of Biochemistry and Molecular
Genetics, University of Colorado Health Sciences Center, Denver,
Colorado 80262,1 and
Department of
Biology, Indiana University, Bloomington, Indiana
474052
Received 6 July 1998/Returned for modification 9 September
1998/Accepted 16 September 1998
Many Caenorhabditis elegans genes exist in operons in
which polycistronic precursors are processed by cleavage at
the 3' ends of upstream genes and trans splicing 100 to 400 nucleotides away, at the 5' ends of downstream genes, to
generate monocistronic messages. Of the two spliced leaders, SL1 is
trans spliced to the 5' ends of upstream genes, whereas SL2
is reserved for downstream genes in operons. However, there are
isolated examples of what appears to be a different sort of operon, in
which trans splicing is exclusively to SL1 and there is no
intercistronic region; the polyadenylation signal is only a few base
pairs upstream of the trans-splice site. We have analyzed
the processing of an operon of this type by inserting the central part
of mes-6/cks-1 into an SL2-type operon. In this novel
context, cks-1 is trans spliced only to SL1,
and mes-6 3'-end formation occurs normally, demonstrating that this unique mode of processing is indeed intrinsic to this kind of
operon, which we herein designate "SL1-type." An exceptionally long
polypyrimidine tract found in the 3' untranslated regions of the
three known SL1-type operons is shown to be required for the
accumulation of both upstream and downstream mRNAs. Mutations of the
trans-splice and poly(A) signals indicate that the two processes are independent and in competition, presumably due to their
close proximity, raising the possibility that production of upstream
and downstream mRNAs is mutually exclusive.
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
SL1 trans Splicing and 3'-End Formation
in a Novel Class of Caenorhabditis elegans
Operon

*
Corresponding author. Mailing address: Department of
Biochemistry and Molecular Genetics, University of Colorado Health
Sciences Center, 4200 E. 9th Ave., Denver, CO 80262. Phone: (303)
315-8181. Fax: (303) 315-8215. E-mail:
blumentt{at}essex.uchsc.edu.
Present address: Department of Molecular Genetics and Microbiology,
RWJ Medical School, UMDNJ, Piscataway, NJ 08854.
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