A micronucleus-specific sequence exists in the 5'-upstream region of calmodulin gene in Tetrahymena thermophila.
Tetrahymena thermophila possesses a transcriptionally inactive micronucleus and an active macronucleus. Both nuclei are developed from micronucleus-derived germ nuclei during conjugation. Extensive DNA rearrangement and transcriptional activation are known to be involved in macronuclear development, but little has been known about these processes in a particular functional gene. Therefore the micro- and macronuclear genomic DNAs for calmodulin gene were analyzed. A 1,384 bp micronucleus-specific sequence located about 3.5 kb upstream of calmodulin gene has been found, suggesting DNA rearrangement during macronuclear development. The micronucleus-specific sequence had 85% A + T, no extensive ORF, ATTAs at both ends, and two palindromic structures just outside of both ends. Interestingly, the micronucleus-specific sequence included a T-rich tract, T16CT5, in the middle, and a nearly complementary A-rich tract, A5TA10GA5, existed 7 bp upstream from the initiation codon. In addition, there was a 20 bp repetitive sequence TAAT(TAAC)4 about 100 bp upstream of the micronucleus-specific sequence and also in the promoter region of calmodulin gene. Although the functional significance of the micronucleus-specific sequence remains unclear, T16CT5 and TAAT(TAAC)4 elements might exert an influence on transcription of the calmodulin gene. Stringent Southern hybridization revealed that this micronucleus-specific sequence or very similar sequence(s) were abundant in the Tetrahymena micronuclear genome.
Institute of Biological Sciences, University of Tsukuba, Ibaraki, Japan.
M
M
Katoh
M
M
Hirono
T
T
Takemasa
M
M
Kimura
Y
Y
Watanabe
D000818:Animals; D001482:Base Composition; D001483:Base Sequence; D015139:Blotting, Southern; D002147:Calmodulin / Q000235:genetics*; D002467:Cell Nucleus / Q000737:chemistry; D015246:Deoxyribonuclease EcoRI; D015252:Deoxyribonucleases, Type II Site-Specific; D015321:Gene Rearrangement; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D011401:Promoter Regions, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D016808:Tetrahymena thermophila / Q000235:genetics*
D002147:Calmodulin; D015246:Deoxyribonuclease EcoRI; D015252:Deoxyribonucleases, Type II Site-Specific; C027440:GATATC-specific type II deoxyribonucleases