خط مشی دسترسیدرباره ماپشتیبانی آنلاین
ثبت نامثبت نام
راهنماراهنما
فارسی
ورودورود
صفحه اصلیصفحه اصلی
جستجوی مدارک
تمام متن
منابع دیجیتالی
رکورد قبلیرکورد بعدی
Document Type:Latin Dissertation
Language of Document:English
Record Number:53060
Doc. No:TL23014
Call number:‭3194579‬
Main Entry:Mohammad Mohammad
Title & Author:Novel mechanism for targeting of trans-acting factors to the Tetrahymena thermophila rDNA repliconMohammad Mohammad
College:The Texas A&M University System Health Science Center
Date:2005
Degree:Ph.D.
student score:2005
Page No:205-205 p.
Abstract:DNA replication is a highly regulated process and governed by the cell cycle machinery, such that chromosomes are replicated once and only once per cell cycle. The question of what determines whether a DNA sequence serves as specific site for replication initiation is largely unanswered in eukaryotes. In the replicon model (bacteria and viruses), specific proteins (initiators) recognize specific DNA sequences (replicators) to control replication initiation. While this model holds true for eukaryotes, the regulation of replication initiation is complex in eukaryotic model systems. For example, the DNA sequences of replicators show little conservation and the key initiator (ORC) binds DNA by distinct mechanisms in different model eukaryotes. I utilized the rDNA minichromosome replicon of Tetrahymena thermophila to further our understanding of the interaction between cis-acting replicators and trans-acting initiation factors. I employed a biochemical approach to characterize protein interactions with type I elements; which are essential genetic determinants for rDNA metabolism. Consequently, TIF1-4 ( t ype I binding f actors 1 through 4) were characterized. Results suggest that complex temporal interactions occur between the rDNA origin and TIF1-4 in vivo . Interestingly, TIF3 binds with high affinity to the C3 rDNA allele, which is preferentially replicated when it co-exists with B rDNA molecules in macronucleus. I focused on a novel origin-binding complex, TIF4 that shares features with the eukaryotic key initiator (ORC). TIF4 is implicated in the cell cycle-controlled replication and amplification of the rDNA minichromosome. Experiments on TIF4 complex revealed an unprecedented mechanism for association with its DNA target. Most significantly, TIF4 is a ribonucleoprotein (RNP) complex. Its RNA subunit corresponds to the 3' terminus of 26S ribosomal RNA (termed 26T), suggesting a new role for ribosomal RNA in chromosome biology. In vitro DNA binding activity is dependent on this RNA subunit that forms RNA:DNA hybrid with DNA. Also, TIF4 complex is selectively targeted to the rDNA origin in vivo . Thus, these studies suggest a new mechanism in which proteins are targeted to specific DNA sites in the chromosome by an associated RNA subunit. I propose that TIF4 through its RNA subunit connects the physiology of ribosomal RNA to rDNA replication control.
Subject:Biological sciences; Tetrahymena thermophila; DNA replication; trans-acting; rDNA; Molecular biology; Cellular biology; Genetics; 0369:Genetics; 0307:Molecular biology; 0379:Cellular biology
Added Entry:G. M. Kapler
Added Entry:The Texas A&M University System Health Science Center