BRANCHES OF BIOLOGY

May 20th, 2015
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Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. 1. Aerobiology — the study of airborne organic particles 2. Agriculture — the study of producing crops from the land, with an emphasis on practical applications

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Objective #36: The Mechanism of Regulating Gene Expression in Eukaryotes.b. Processing ControlI. U1A Protein Inhibits Polyadenylation of Its Pre-mRNAU1A protein binds to a 7-basesequence in the snRNA component of U1 snRNP. Thepre-mRNAencoding U1A itself also contains two copies of this 7-base sequence (one with a single-base change) justupstreamof its polyadenylation signal. When a U1A protein molecule is bound to each copy of this 7-base sequence in a U1A pre-mRNA in anin vitrosystem containing poly(A) polymerase and all the factors necessary for cleavage and polyadenylation, cleavage occurs but addition of the poly(A) tail does not.Note that the sequence of the upstream polyadenylation signal differs slightly from the usual one (AAUAAA). This unusual sequence is found in rare pre-mRNAs. The human U1 snRNP-specific U1A protein autoregulates its production by binding its own pre-mRNA and inhibiting polyadenylation. The mechanism of this regulation has been elucidated by in vitro studies. U1A protein is shown not to prevent either binding of cleavage and polyadenylation specificity factor (CPSF) to its recognition sequence (AUUAAA) or to prevent cleavage of U1A pre-mRNA. Instead, U1A protein bound to U1A pre-mRNA inhibits both specific and nonspecific polyadenylation by mammalian, but not by yeast, poly(A) polymerase (PAP). Domains are identified in both proteins whose removal uncouples the polyadenylation activity of mammalian PAP from its

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