Nucleic Acids Research, Vol 25, Issue 10 1883-1889, Copyright © 1997 by Oxford University Press
DC Hoffman and DM Prescott
To learn about the evolution of internal eliminated segments (IESs) and
gene scrambling in hypotrichous ciliates we determined the structure of the
micronuclear (germline) gene encoding DNA polymerasealpha(DNA polalpha) in
Oxytricha trifallax and compared it to the previously published structure
of the germline DNA polalphagene in Oxytricha nova . The DNA polalphagene
of O.trifallax contains 51 macronuclear-destined segments (MDSs) separated
by 50 IESs, compared to 45 MDSs and 44 IESs in the O.nova gene. This means
that IESs and MDSs have been gained and/or lost during evolutionary
divergence of the two species. Most of the MDSs are highly scrambled in a
similar non-random pattern in the two species. We present a model to
explain how IESs, non-scrambled MDSs and scrambled MDSs may be added and/or
eliminated during evolution. Corresponding IESs in the two species differ
totally in sequence, and junctions between MDSs and IESs are shifted by
1-18 bp in O.trifallax compared to the O.nova gene. In both species a short
region of the gene is distantly separated from the main part of the gene.
Comparison of the gene in the two species shows that IESs and scrambling
are highly malleable over evolutionary time.
ARTICLES
Evolution of internal eliminated segments and scrambling in the micronuclear gene encoding DNA polymerase alpha in two Oxytricha species
Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309-0347, USA.
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