A novel family of mobile genetic elements is limited to the germline genome in Tetrahymena thermophila.
In the ciliated protozoan Tetrahymena thermophila, extensive DNA elimination is associated with differentiation of the somatic macronucleus from the germline micronucleus. This study describes the isolation and complete characterization of Tlr elements, a family of approximately 30 micronuclear DNA sequences that are efficiently eliminated from the developing macronucleus. The data indicate that Tlr elements are comprised of an approximately 22 kb internal region flanked by complex and variable termini. The Tlr internal region is highly conserved among family members and contains 15 open reading frames, some of which resemble genes encoded by transposons and viruses. The Tlr termini appear to be long inverted repeats consisting of (i) a variable region containing multiple direct repeats which differ in number and sequence from element to element and (ii) a conserved terminal 47 bp sequence. Taken together, these results suggest that Tlr elements comprise a novel family of mobile genetic elements that are confined to the Tetrahymena germline genome. Possible mechanisms of developmentally programmed Tlr elimination are discussed.
Wuitschick
Jeffrey D
JD
Department of Biology, Marquette University, Milwaukee, WI 53201-1881, USA.
Gershan
Jill A
JA
Lochowicz
Andrew J
AJ
Li
Shuqiang
S
Karrer
Kathleen M
KM
D000595:Amino Acid Sequence; D000818:Animals; D001482:Base Composition; D001483:Base Sequence; D015139:Blotting, Southern; D002467:Cell Nucleus / Q000235:genetics; D017124:Conserved Sequence / Q000235:genetics; D004251:DNA Transposable Elements / Q000235:genetics*; D016054:DNA, Protozoan / Q000235:genetics*; D018503:Genome, Protozoan; D015698:Genomic Library; D005854:Germ Cells / Q000166:cytology / Q000378:metabolism*; D018095:Germ-Line Mutation / Q000235:genetics; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics*; D016366:Open Reading Frames / Q000235:genetics; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics; D016415:Sequence Alignment; D016808:Tetrahymena thermophila / Q000737:chemistry / Q000166:cytology / Q000235:genetics*
D004251:DNA Transposable Elements; D016054:DNA, Protozoan; D015800:Protozoan Proteins