How have introns evolved? Did they occur early in the prebiotic world and contribute to the formation of ancient genes by """"""""exon shuffling,"""""""" or have they been inserted into genes as mobile genetic elements throughout evolution? Important insights into intron evolution have come from analysis of the chloroplast genome of the photosynthetic protist Euglena gracilis, which contains at least 120 introns, several introns-within-introns, known as """"""""twintrons"""""""", and complex twintrons formed from 3 or 4 individual introns which are sequentially spliced. A detailed study of the group III introns and twintrons of Euglena is proposed.
The specific aims i nclude: (1) Characterization of additional group III introns and twintrons and their RNA processing pathways, (2) Determination of the extent and importance of alternative splicing of group III introns, and specifically whether alternative splicing results in alternative polypeptides products from a single gene, (3) A study of how group III introns and twintrons have evolved, addressed through a comparative analysis of group III introns in species related to Euglena gracilis, (4) Studies on a gene within a twintron, orf458 of the psbC locus, to assess if this gene may have a role in the mobility or splicing of group III introns, (5) Development of a system for transformation of Euglena chloroplasts, in order to study cis- and trans-acting factors in intron and twintron splicing in transgenic plastids, and (6) Attempts to develop an in vitro group III intron splicing system. This work is addressed at understanding fundamental question about the origins of introns, splicing mechanisms, and alternative splicing.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM035665-11
Application #
2177998
Study Section
Molecular Biology Study Section (MBY)
Project Start
1985-02-01
Project End
1997-06-30
Budget Start
1995-07-01
Budget End
1996-06-30
Support Year
11
Fiscal Year
1995
Total Cost
Indirect Cost
Name
University of Arizona
Department
Biochemistry
Type
Schools of Arts and Sciences
DUNS #
City
Tucson
State
AZ
Country
United States
Zip Code
85721
Sheveleva, Elena V; Hallick, Richard B (2004) Recent horizontal intron transfer to a chloroplast genome. Nucleic Acids Res 32:803-10
Sheveleva, Elena V; Giordani, Nicole V; Hallick, Richard B (2002) Identification and comparative analysis of the chloroplast alpha-subunit gene of DNA-dependent RNA polymerase from seven Euglena species. Nucleic Acids Res 30:1247-54
Doetsch, N A; Favreau, M R; Kuscuoglu, N et al. (2001) Chloroplast transformation in Euglena gracilis: splicing of a group III twintron transcribed from a transgenic psbK operon. Curr Genet 39:49-60
Doetsch, N A; Thompson, M D; Favreau, M R et al. (2001) Comparison of psbK operon organization and group III intron content in chloroplast genomes of 12 Euglenoid species. Mol Gen Genet 264:682-90
Doetsch, N A; Thompson, M D; Hallick, R B (1998) A maturase-encoding group III twintron is conserved in deeply rooted euglenoid species: are group III introns the chicken or the egg? Mol Biol Evol 15:76-86
Stevenson, J K; Hallick, R B (1994) The psaA operon pre-mRNA of the Euglena gracilis chloroplast is processed into photosystem I and II mRNAs that accumulate differentially depending on the conditions of cell growth. Plant J 5:247-60
Hong, L; Hallick, R B (1994) Gene structure and expression of a novel Euglena gracilis chloroplast operon encoding cytochrome b6 and the beta and epsilon subunits of the H(+)-ATP synthase complex. Curr Genet 25:270-81
Drager, R G; Hallick, R B (1993) A novel Euglena gracilis chloroplast operon encoding four ATP synthase subunits and two ribosomal proteins contains 17 introns. Curr Genet 23:271-80
Drager, R G; Hallick, R B (1993) A complex twintron is excised as four individual introns. Nucleic Acids Res 21:2389-94
Copertino, D W; Shigeoka, S; Hallick, R B (1992) Chloroplast group III twintron excision utilizing multiple 5'- and 3'-splice sites. EMBO J 11:5041-50

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