Analysis of a scrambled gene: the gene encoding alpha-telomere-binding protein in Oxytricha nova.
Following cell mating in ciliates, a copy of the micronuclear genome is processed into a new macronucleus through massive cutting, reordering, splicing, elimination, and amplification of the DNA. DNA processing includes the deletion of short interrupting elements called internal eliminated sequences (IESs), followed by the splicing of the remaining segments, known as macronuclear destined sequences (MDSs). The MDSs in some micronuclear genes, such as actin I, are scrambled and must be reordered during IES removal and MDS splicing to yield a functional gene. Here, we describe the cloning, sequencing, and characterization of a different scrambling pattern for the gene that encodes the alpha subunit of the telomere-binding protein of Oxytricha nova. The micronuclear gene is made up of 14 MDSs in the scrambled order 1-3-5-7-9-11-2-4-6-8-10-12-13-14. Only the scrambled version is present in the micronucleus, and only the unscrambled version is present in the macronucleus. We propose that unscrambling occurs by homologous recombination guided by pairs of direct repeats at MDS-IES junctions. The patterned array of scrambling may be a clue to the origin of scrambling in this gene.
Mitcham
J L
JL
University of Colorado, Department of Molecular, Cellular, and Developmental Biology, Boulder 80309-0347.
Lynn
A J
AJ
Prescott
D M
DM
D000818:Animals; D001483:Base Sequence; D015139:Blotting, Southern; D003001:Cloning, Molecular; D016054:DNA, Protozoan / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics*; D005796:Genes; D008969:Molecular Sequence Data; D016813:Oxytricha / Q000235:genetics*; D016133:Polymerase Chain Reaction; D015800:Protozoan Proteins / Q000235:genetics*; D011995:Recombination, Genetic / Q000235:genetics; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D012689:Sequence Homology, Nucleic Acid
D016054:DNA, Protozoan; D004268:DNA-Binding Proteins; D015800:Protozoan Proteins