Eukaryotes regulation

Cyclins and Cdks are conserved among all multicellular eukaryotes. Regulation of transcription of genes encoding components of the cell-cycle machine by cyclin-Cdks, in cooperation with the E2F transcription factors, are, in principle, the same in vertebrates and invertebrates. Furthermore, at least one of the two families of Cdk inhibitors in vertebrates is also present in Drosophila. 

In eukaryotes, regulation of protein synthesis may occur by modification of DNA or at the level of transcription or translation. 

In prokaryotes, mRNA synthesis can be controlled simply by regulating initiation of transcription. In eukaryotes, mRNA is formed from a primary transcript followed by a series of processing events (e.g., intron excision, polyadenylylation). Eukaryotes regulate not only transcription initiation but the various stages of processing as well. 

Sometimes different organisms regulate similar pathways in different ways. For example, ATCase is the major control point in the pyrimidine pathway synthesis in bacteria, whereas eukaryotes regulate the synthesis of carbamoyl phosphate (Figure 11,35). In mammals, the carbamoyl phosphate synthetase n is inhibited by UDP, UTP, CTP, dUDP, and UDP-glucose. 

Eukaryotes Regulation of gene expression at the level ofDNA. In eukaryotes, activation of a gene requires changes in the state of chromatin (chromatin remodeling) that are facilitated by acetylation of histones and methylation of bases. These changes in DNA determine which genes are available for transcription. 

Eukaryotic regulation. In eukaryotes, the transcriptional regulation is substantially more complicated, such as ... 

In eukaryotes, regulated secretion, sequestration to and protein release from organelles, as well as mRNA stabihzation, were not understood. 

It has also been suggested that some genes which code for protein inductors (or histones) may be able to regulate the activity of another gene system by acting at the transcriptional level (i.e., dosage compensation). Therefore, some elements of the Jacob and Monod scheme for bacteria can be included in the scheme of control in eukaryotes. These similar elements, however, represent only one component of the complex system of eukaryotic regulation. 

The Ca2+-binding subunit TN-C is homologous to calmodulin with four EF-hands. In contrast to calmodulin, which is ubiquitously expressed in multicellular eukaryotic organisms and interacts with many targets, troponin specifically regulates muscle contraction. There are some structural differences between Troponin C in skeletal and cardiac muscles reflecting their physiological differences. 

In cyclic nucleotide-regulated channels, this domain serves as a high-affinity binding site for 3-5 cyclic monophosphates. The CNBD of channels has a significant sequence similarity to the CNBD of most other classes of eukaryotic cyclic nucleotide receptors and to the CNBD of the prokaryotic catabolite activator protein (CAP). The primary sequence of CNBDs consists of approximately 120 amino acid residues forming three a-helices (oA-aC) and eight (3-strands ( 31- 38). 

Researchers found that NAD serves as a substrate in poly(ADP-ribose) synthesis, a reaction important for DNA repair processes. In addition, it takes part in mono (ADP-ribosyl)ation reactions that are involved in endogenous regulation of many aspects of signal transduction and membrane trafficking in eukaryotic cells. 

The multiple sites that serve as origins for DNA replication in eukaryotes are poorly defined except in a few animal viruses and in yeast. However, it is clear that initiation is regulated both spatially and temporaUy, since clusters of adjacent sites initiate rephcation synchronously. There are suggestions that functional domains of chromatin replicate as intact units, implying that the origins of rephcation are specificaUy located with respect to transcription units. 

All steps—from changes in DNA template, sequence, and accessibility in chromatin to RNA stability—are subject to modulation and hence are potential control sites for eukaryotic gene regulation. 

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