Spring 09 lecture 33

Spring 09 lecture 33 - Control of gene expression: overall...

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Transcription initiation Direct influence of A and R on initiation Activators (A), repressors (R) and remodeling proteins and chromatin structure Methylation Hormones and other “external” signals RNA processing Capping and polyadenylation Alternative splicing and trans-splicing Transport through the nuclear pore Posttranscriptional / pretranslational control (events on/with mRNA before ribosomes) Localization of mRNA RNA editing Post-transcriptional silencing by siRNA or miRNA Translational control switch RNA stability (degradation and stabilization) Translational control (mRNA/ribosomes) Phosphorylation of translation initiation factors Upstream AUG codons IRES Protein activity control Posttranslational modification and transport Control of gene expression: overall
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, possible cleaving as well Protein activity control First step: posttranslational modification and transport
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Protein modifications Modifications necessary for transport from the cytoplasm Proteins that are membrane bound or are destined for secretion (e.g. TFs and protein hormones) are   synthesized by ribosomes associated with the membranes of the endoplasmic   reticulum (ER). The ER associated with ribosomes is termed rough ER (RER). This class of proteins all contain a N- terminus - signal sequence or signal peptide; transport is co-translational Proteins destined for organelles : different signal sequences at N-terminus Proteolytic Cleavage Most proteins undergo proteolytic cleavage following translation. The simplest form - removal of the first methionine.
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Acylation In most cases acetyl group is added to the N-terminal amino acid (after first Met is removed) Acetyl-CoA is the acetyl donor for these reactions. Glycosilation Glycoproteins consist of proteins with covalently linked sugars (glucose, galactose, mannose, fucose, GalNAc, GlcNAc …) Consensus AA for addition: Asn – X – Ser/Thr Methylation Post-translational methylation occurs at lysine residues in some proteins The activated methyl donor is S-adenosylmethionine. Examples: calmodulin and cytochrome c Prenylation Addition of the compounds derived from the cholesterol biosynthetic pathway examples: oncogenic GTP-binding and hydrolyzing protein Ras
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Phosphorylation Post-translational phosphorylation is one of the most common protein   modifications Occurs as a mechanism to regulate the biological activity of a protein and as such – transient: phosphate (or more than one in many cases) is added and later removed (or transferred to other protein) The enzymes involved: Kinases: transfer a phosphate group from a donor (usually ATP) to the acceptor (protein) Phosphorylases: transfer a phosphate group from an inorganic phosphate Phosphatases: remove phosphates In animal cells serine, threonine and tyrosine are the amino acids subject to phosphorylation (-OH group - hydrophilic and “phosphorylable” site)
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Spring 09 lecture 33 - Control of gene expression: overall...

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