Identification of single nucleotide mutations that prevent developmentally programmed DNA elimination in Paramecium tetraurelia.
The excision of internal eliminated sequences (IESs) occurs during the differentiation of a new somatic macronuclear genome in ciliated protozoa. In Paramecium tetraurelia, IESs show few conserved features with the exception of an invariant 5'-TA-3' dinucleotide that is part of an 8-bp inverted terminal repeat consensus sequence with similarity to the ends of mariner/Tc1 transposons. We have isolated and analyzed two mutant cell lines that are defective in excision of individual IESs in the A-51 surface antigen gene. Each cell line contains a mutation in the flanking 5'-TA-3' dinucleotide of IES6435 and IES1835 creating a 5'-CA-3' flanking sequence that prevents excision. The results demonstrate that the first position of the 5'-TA-3' is required IES excision just as previous mutants have shown that the second position (the A residue) is required. Combining these results with other Paramecium IES mutants suggests that there are few positions essential for IES excision in Paramecium. Analysis of many IESs reveals that there is a strong bias against particular nucleotides at some positions near the IES termini. Some of these strongly biased positions correspond to known IES mutations, others correlate with unusual features of excision.
Matsuda
Atsushi
A
Department of Biochemistry, Purdue University, 175 South University Street, West Lafayette, Indiana 47907-2063, USA.
Mayer
Kimberly M
KM
Forney
James D
JD
D000818:Animals; D000953:Antigens, Protozoan / Q000235:genetics; D004251:DNA Transposable Elements / Q000235:genetics; D016054:DNA, Protozoan / Q000235:genetics*; D016805:Paramecium tetraurelia / Q000235:genetics* / Q000254:growth & development; D017354:Point Mutation; D011995:Recombination, Genetic; D012091:Repetitive Sequences, Nucleic Acid
D000953:Antigens, Protozoan; D004251:DNA Transposable Elements; D016054:DNA, Protozoan