Conserved cis- and trans-acting determinants for replication initiation and regulation of replication fork movement in tetrahymenid species.
The rDNA minichromosomes of Tetrahymena thermophila and Tetrahymena pyriformis share a high degree of sequence similarity and structural organization. The T.thermophila 5' non-transcribed spacer (5' NTS) is sufficient for replication and contains three repeated sequence elements that are conserved in T.pyriformis , including type I elements, the only known determinant for replication control. To assess the role of conserved sequences in replication control, structural and functional studies were performed on T.pyriformis rDNA. Similar to T.thermophila , replication initiates exclusively in the 5' NTS, localizing to a 900 bp segment. Elongating replication forks arrest transiently at one site which bears strong similarity to a tripartite sequence element present at fork arrest sites in T.thermophila rDNA. An in vitro type I element binding activity indistinguishable from the T.thermophila protein, ssA-TIBF, was detected in T.pyriformis extracts. The respective TIBF proteins bind with comparable affinity to type I elements from both species, suggesting that in vivo recognition could cross species boundaries. Despite these similarities, the T.pyriformis 5' NTS failed to support replication in transformed T.thermophila cells, suggesting a more complex genetic organization than previously realized.
Yue
M
M
Department of Medical Biochemistry and Genetics, Texas A&M Health Science Center, College Station, TX 77843-1114, USA.
Reischmann
K P
KP
Kapler
G M
GM
D000818:Animals; D001483:Base Sequence; D002875:Chromosomes / Q000235:genetics; D017124:Conserved Sequence; D015342:DNA Probes; D004261:DNA Replication / Q000235:genetics*; D016054:DNA, Protozoan / Q000096:biosynthesis / Q000235:genetics; D004275:DNA, Ribosomal / Q000096:biosynthesis* / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism*; D016521:Electrophoresis, Gel, Pulsed-Field; D015180:Electrophoresis, Gel, Two-Dimensional; D018014:Gene Transfer Techniques; D020161:Physical Chromosome Mapping; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics*; D018741:Replication Origin / Q000235:genetics; D013769:Tetrahymena pyriformis / Q000235:genetics*; D016808:Tetrahymena thermophila / Q000235:genetics*
D015342:DNA Probes; D016054:DNA, Protozoan; D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins