Genomic intron densities are highly variable across species, ranging from many introns per transcript in humans to fewer than one per transcript in some microbes. The extremophilic red alga, Cyanidioschyzon merolae, has taken intron reduction to an extreme, harboring only ~40 introns in its 5000-gene genome. This raises the question of whether this alga contains the canonical set of splicing machinery, which in humans comprises 5 small, nuclear RNAs and over 200 proteins.

On September 21^st, Prof. Stephen D. Rader from the University of Northern British Columbia, Canada, will talk about ‘The Highly Reduced Spliceosome of C. merolae’. To study the biological role of this tiny intron complement, Stephen and his group have characterized the splicing machinery in C. merolae. Surprisingly, it is completely lacking the U1 snRNP, comprises only ~40 core proteins, has but a single LSm complex, and appears to have an RNA degradation complex associated with it.

The unexpected observation of apparent splicing regulatory proteins raised the possibility that the splicing events in C. merolae, few though they are, are regulated in response to environmental conditions or other cues. Stephen will discuss current efforts to investigate this possibility. The small size of the C. merolae spliceosome make this a promising system in which to study core features of the splicing pathway, as well as the evolutionary pressures that result in reduced splicing systems.