Eukaryotic gene expression tissue-specific

Inferential evidence supports a role for nonhistone proteins in regulating eukaryotic gene expression (O Malley et al., 1977). The nonhistone proteins increase in amount in tissues carrying out RNA transcription, in the face of unchanged histone levels. The nonhistone proteins also exhibit a greater heterogeneity than the five histone proteins and possess DNA binding specificity. Nonetheless, a demonstration of an unequivocal role for these proteins will depend upon more definitive evidence than is presently available. 

However, promoters are not the only types of cis-acting DNA sequences. Eukaryotes and their viruses also contain enhancers. These DNA sequences, although not promoters themselves, can enormously increase the effectiveness of promoters. Interestingly, the positions of enhancers relative to promoters are not fixed they can vary substantially. Enhancers play key roles in regulating gene expression in a specific tissue or developmental stage (Section 31.2.4). 

In vivo methylation of the side chains of specific arginines, histidines, and lysines in proteins is a common phenomenon in nature involving numerous classes of proteins in both prokaryotic and eukaryotic cells. - Methylation has been most well studied in histones, with distinct lysine residues mono-, di-, or tri-methylated playing a major role in the regulation of gene expression, DNA replication, and repair. Methylated amino acids have often been determined in protein and tissue hydrolysates using amino acids analyzers and through cells radiolabeled with [methyl- H] methionine. 

Post-translational modifications, such as phosphorylation, complex glycosylation, and lipidation, typically occur in eukaryotic organisms. Therefore, their expression in prokaryotic systems like Escherichia coli is difficult. However, it should be noted that via clever engineering and coexpression of specific enzymes, access can be granted to specific lipidated proteins via expression in bacteria, for example, via the expression of A -myristoyltransferase in E. coli Eukaryotic systems that can be used for the expression of post-translationally modified proteins are yeast and Dictyostelium discoidum. Furthermore, lipidated proteins, such as the Rah proteins, can be obtained via purification from tissue sources or from membrane fractions of insect cells that had been infected with baculovirus bearing a Rah gene. ... 

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