Characterization of a bi-directional promoter for divergent transcription of a PHD-zinc finger protein gene and a ran gene in the protozoan pathogen Giardia lamblia.
We showed previously that transcription of the ran gene in Giardia lamblia is regulated by an AT-rich initiator. In the present study, the ran initiator was found to regulate transcription of a neighbouring PHD zinc-finger protein gene. Deletion and scanning mutagenesis of the phd promoter in a firefly luciferase reporter system showed that the promoter activity is determined by multiple single-stranded T-tract DNA elements distributed into a distal domain spanning the ran initiator (-134/-103) and a proximal domain (-88/-48) spanning phd messenger RNA (mRNA) start sites (-74, -55 and -53 relative to the first ATG). The promoter activity is repressed by the single T-tract element on a non-template strand of the ran initiator, and is activated by closely spaced T-tract elements on the opposite strand. The T-tract elements in the phd and ran initiators compete for similar ssDNA binding proteins. Mutation of -47/-42 resulted in dramatic reduction of luciferase activity without changing luciferase mRNA levels, indicating the potential involvement of a regulatory mechanism in PHD protein translation. These findings suggest that G. lamblia uses multiple copies of a T-tract element as both core and distal elements in regulating transcription initiation, and that expression of the phd gene is regulated at multiple levels.
Ong
Shiou-Jeng
SJ
Department of Parasitology, College of Medicine, National Taiwan University, Taipei, Taiwan, Republic of China.
Huang
Li-Chin
LC
Liu
Hsing-Wei
HW
Chang
Shih-Chia
SC
Yang
Yen-Ching
YC
Bessarab
Irina
I
Tai
Jung-Hsiang
JH
D020121:5' Untranslated Regions; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D021901:DNA, Intergenic; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D016829:Giardia lamblia / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic; D016335:Zinc Fingers / Q000235:genetics*; D020931:ran GTP-Binding Protein / Q000235:genetics* / Q000378:metabolism
D020121:5' Untranslated Regions; D021901:DNA, Intergenic; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; C455502:Phd protein, Giardia lamblia; D015800:Protozoan Proteins; D020931:ran GTP-Binding Protein