Transcriptional regulation expression

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). 

It is likely that transcriptional regulation of Na /H exchanger gene expression is responsible for some of these observations, a possibility that could be first tested by examining the structure and function of the gene promoter. 

Song J, T Xia, RA Jensen (1999) PhhB, a Pseudomonas aeruginosa homolog of mammalian pterin 4a-carbi-nolamine dehydratase/DCcoH, does not regulate expression of phenylalanine hydroxylase at the transcriptional level. J Bacterial 181 2789-2796. 

Using human hepatoma-derived cell lines Kong et al. [268] showed that berberine increased mRNA and protein as well as the function of hepatic linear low density lipoprotein receptor (LDLR). It does not stimulate the transcription of LDLR, as the LDLR promoter activity was not increased by this compound. Post-transcriptional regulation appears to be the main working mechanism underlying the effect of this alkaloid on LDLR expression. It was proposed that berberine can be used as a monotherapy to treat hypercholes-terolemic patients [268]. Very recently it was observed [269] that berberine reduces cholesterol and Upid accumulations in plasma as well as Uver. 

Figure 1. Hierarchy of control of gene expression. A total of about 50,000 to 100,000 genes are necessary to encode a mammal, most of which encode housekeeping, structural component, or terminal differentiation gene products. Transcription factor genes regulate expression of the lower-level genes and are in turn controlled by other upper-level transcription factors.

A mbros Less is known about how cki-1 is shut off in VPCs than about how cki-1 is turned on in these cells. However, when we misexpress lin-14 late in development, it will maintain cki-1 expression later than in the normal vulval lineage. Therefore, extinction of cki-1 expression in VPCs is influenced by some activity that is in turn dependent on lin-14 down-regulation. All our cki-1 expression constructs retain the 3hUTR of cki-1 (Hong et al 1998), and so the dynamic cki-1 expression we observe could reflect post-transcriptional regulation in addition to transcription regulation. 

Vine, AL, YM Leung, and JS Bertram. 2005. Transcriptional regulation of connexin 43 expression by retinoids and carotenoids similarities and differences. Mol Carcinog 43 75-85. 

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