简介

Molecular Parasitology-Anything and Everything about the Spliced Leader RNA Our research focuses on the nuclear gene expression of the kinetoplastid protozoa, commonly known as trypanosomes. These mainly parasitic protists are found in a diverse range of host organisms, including insects, fish, molluscs, plants, reptiles and mammals, and are the causative agents of medical and agricultural afflictions. In humans, diseases such as African Sleeping Sickness, Leishmaniasis, and Chagas Disease are caused by trypanosomatid infections, afflicting millions of people worldwide. Our work is specialized in the characterization, expression and action of a key player in the expression of all nuclear protein coding genes called the Spliced Leader (SL) RNA, or mini-exon RNA. The ~100-nt SL RNA contains a 39-nt exon that is transferred via a trans-splicing reaction to the 5' end of every nuclear mRNA. The trans-splicing of the SL exon is critical for trypanosomatids, as their mRNAs are encoded in a polycistronic fashion and cannot receive their 5' caps structures directly. Because this form of trans-splicing is not found in the human or insect hosts, a complete understanding of the genesis of the SL RNA and the trans-splicing process may lead to clinical treatments for trypanosome infections. The SL RNA gene is found in a head-to-tail tandem array, which we have used to develop a universal trypanosomatid PCR assay. Using this assay we have amplified over 50 different trypanosomatids and close relatives, providing us with a valuable database for inter-genus and inter-species comparisons, as well as a powerful diagnostic tool. Perhaps the most interesting finding is the extent to which the 39-nt SL sequence is conserved, implying a critical role for this sequence block that extends throughout the Family. The SL RNA gene represents the first and only RNA polymerase II transcript with a defined promoter in the trypanosomatids to date. We have identified two elements of the SL RNA gene promoter of lizard leishmania Leishmania tarentolae to the nucleotide level and are in the process of biochemically purifying interacting factors, as well as cloning likely transcription factors as they appear in the genome database. Our experiments have examined the SL RNA gene transcription termination element, along with several processing steps for the SL RNA itself including 3' trimming and 5' end methylations resulting in the 'cap4' structure. Our current model for the processing of the SL RNA includes a cytoplasmic maturation stage, a matter of some debate in our field. One of the questions we would like to resolve is the role of the conserved sequence element within the SL exon. Since we have demonstrated that it is not required for transcription, termination, 3'- or 5'-processing, or trans-splicing itself, we are exploring the role of the SL in translation and in nucleosome structure.