Cloning of two putative Giardia lamblia glucosamine 6-phosphate isomerase genes only one of which is transcriptionally activated during encystment.
The biosynthesis of the carbohydrate component of the cyst wall of the protozoan parasite Giardia lamblia, a polymer of N-acetylgalactosamine (GalNac), is by a pathway that is initiated with the conversion of fructose 6-phosphate to glucosamine 6-phosphate by an aminating isomerase, glucose 6-phosphate isomerase. This enzyme appears only after Giardia trophozoites are induced to start the production of cyst wall components after bile is added. To investigate whether induction of glucosamine 6-phosphate isomerase is by protein modification or by transcription activation, its gene was cloned and sequenced. Two genes, gpi1 and gpi2, encoding putative glucosamine 6-phosphate isomerases were identified but one, gpi1 was expressed. The transcript for gpi1 appeared not earlier than 6 h after cells were induced with bile salts. These results show that the first enzyme in the pathway leading to GalNac synthesis in encysting Giardia cyst wall biosynthesis is under transcriptional control.
Van Keulen
H
H
Department of Biological, Geological and Environmental Sciences, Cleveland State University, Ohio 44115, USA. vankeule@biology.csuohio.edu
Steimle
P A
PA
Bulik
D A
DA
Borowiak
R K
RK
Jarroll
E L
EL
D019747:Aldose-Ketose Isomerases / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D016054:DNA, Protozoan; D004790:Enzyme Induction; D017125:Genes, Protozoan; D016829:Giardia lamblia / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D011817:Rabbits; D017386:Sequence Homology, Amino Acid; D015533:Transcriptional Activation
D016054:DNA, Protozoan; C020582:glucosamine-6-phosphate isomerase; D019747:Aldose-Ketose Isomerases