In Vitro and in Vivo Differentiation of L.Mexicana-Hsp70 Gene Expression

Expression of heat shock proteins (Hsp’s) is a universal response to exposure of cells to stress of various kinds. It is believed to play an important role in protecting the organism against unphysiological growth conditions, and in acquisition of thermotolerance, through mechanisms which are still not uniquely agreed upon. For review see references1–3. Most abundant are proteins of Mr 70 and 83–90 Kd, which are both highly conserved throughout evolution. Proteins of the Hsp70 family all share the characteristic of binding to ATP4–6, and are believed to be involved in prevention or disruption of hydrophobic aggregates through an ATP-dependent mechanism7. Recently it has also been shown that RNA splicing is interrupted by heat shock and rescued by Hsp70 expression8. Most organisms also produce one or more small heat shock proteins, with Mr of 18–30 Kd. These small Hsp’s show a lower degree of structural conservation among species. In some organisms, heat shock genes are expressed independently of environmental stress at specific stages of development9.