Leishmania mexicana amazonensis: Effect of heat shock on the spliced leader RNA and its ribonucleoprotein particle SL RNP

Trypanosomatid parasites of the genus Leishmania experience a temperature shift from 22-38°C to 33-37°C while being transmitted from the invertebrate vector to the mammalian host. Expression of many protein-coding genes in protozoan parasites that cycle between two hosts have been shown to be thermosensitive, and temperature changes most probably serve as a major regulatory factor during stage differentiation. We present here out studies on effects of physiological temperature shift on the steady-state and nascent synthesis of the spliced leader SL RNA, as well as on its small RNP particle, SL RNP. Northern blot analysis showed no significant changes in the steady-state level of SL RNA at elevated temperatures. Neither were any alterations detected at the two different temperatures in nascent transcription of the SL RNA gene, examined in cells made permeable by treatment with lysolecithin. Fractionation of cell extracts on Cs₂SO₄ gradients indicated that temperature elevation led to changes in SL RNP particles. Alterations in these particles upon heat shock were also observed by separation on polyacrylamide gels, but only in the presence of urea, indicating that the differences caused by elevation of temperature were revealed exclusively under stringent fractionation conditions.