Sequence and expression of the SerJ immobilization antigen gene of Tetrahymena thermophila regulated by dominant epistasis.
In ciliates, variable surface protein genes encoding the immobilization antigen (-ag) are expressed under different environmental conditions, including temperature and salt stress. These i-ags are GPI-linked and coat the entire external surface of the cell, including the cilia. In Tetrahymena thermophila-ag in natural isolates is the result of dominant epistasis masking the expression of the H i-ag ordinarily expressed at 20-36 degrees C. This report describes the expression and sequence of the Ser-ag. J is present on the cell surface up to 38 degrees C; above 38 degrees C SerSeranked by an A-rich 5' UTR and a 3' UTR containing putative mRNA destabilization motifs. The encoded J polypeptide consists of 438 amino acids and is rich in alanine, cysteine, serine and threonine. The N- and resemble signal peptide and GPI-anchor addition sites, respectively. The majority of the molecule consists of four imperfect repeats with 10 periodic cysteines per repeat in the pattern CX(6)CX(2)CX(21)CX(4)CX(13-15)CX(2)CX(18)CX(3)CX(11)CX(9-10). Although H i-ags encoded by paralogous SerH genes have 3.5 imperfect repeats with eight periodic cysteines per repeat, J nevertheless resembles H with respect to amino acid composition, codon usage, N- and C-termini, the arrangement of the cysteine periods, and regulation by mRNA stability. However, despite these similarities and epistasis, the evolutionary relationship between SerH and SerJ is unclear.
Doerder
F P
FP
Department of Biological, Geological and Environmental Sciences, Cleveland State University, Cleveland, OH 44115, USA. f.doerder@csuohio.edu
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D000953:Antigens, Protozoan; D000954:Antigens, Surface / Q000737:chemistry / Q000235:genetics*; D001483:Base Sequence; D015152:Blotting, Northern; D003545:Cysteine / Q000235:genetics; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D016054:DNA, Protozoan / Q000737:chemistry / Q000235:genetics; D004843:Epistasis, Genetic; D005786:Gene Expression Regulation; D008969:Molecular Sequence Data; D015800:Protozoan Proteins; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid / Q000235:genetics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013696:Temperature; D016808:Tetrahymena thermophila / Q000235:genetics*
D000953:Antigens, Protozoan; D000954:Antigens, Surface; D018076:DNA, Complementary; D016054:DNA, Protozoan; D015800:Protozoan Proteins; D012333:RNA, Messenger; C043323:immobilization antigens; D003545:Cysteine