Gene expression regulatory mechanisms

Lacasa, D., Le Liepvre, X., Ferre, P. and Dugail, I., Progesterone stimulates adipocyte determination and differentiation 1/sterol regulatory element-binding protein Ic gene expression, potential mechanism for the lipogenic effect of progesterone in adipose tissue, J Biol Chem 276 (2001) 11512-11516. 

It is very clear that transcriptional control harbors pathways and mechanisms that are not dreamt of in our current paradigms. The integration of chromatin infrastructure into gene expression regulatory pathways, however, is fairly certain to remain at the core of our notions of genome control. 

Clearly, the control of gene expression at the transcriptional level is a key regulatory mechanism controlling carotenogenesis in vivo. However, post-transcriptional regulation of carotenoid biosynthesis enzymes has been found in chromoplasts of the daffodil. The enzymes phytoene synthase (PSY) and phytoene desaturase (PDS) are inactive in the soluble fraction of the plastid, but are active when membrane-bound (Al-Babili et al, 1996 Schledz et al, 1996). The presence of inactive proteins indicates that a post-translational regulation mechanism is present and is linked to the redox state of the membrane-bound electron acceptors. In addition, substrate specificity of the P- and e-lycopene cyclases may control the proportions of the p, P and P, e carotenoids in plants (Cunningham et al, 1996). 

Four fundamental changes induced in host cells will be discussed initially (i) infection-induced cell cycle re-entry (ii) suspension of host cells in apparent G2/M (iii) repression of host muscle gene expression and (iv) further induction of the infected cell phenotype. A clear understanding of these fundamental changes induced by the infection is critical in elucidating the cellular mechanisms involved and, possibly, the host regulatory factors that are interfered with by parasite products. 

The covalent modifications of histone tails such as acetylation, phosphorylation, and ubiquitination have been shown to be reversible. This reversibility help the cells to respond to these regulatory modifications and thereby, influence the gene expression. Methylation of histones however, has been considered to be a relatively stable and irreversible mark on histones. Nevertheless active turnover of methyl groups on histones do exist. One of the possible mechanism of removal of methyl... 

---