2026-09-23T07:00:49Z https://www.ideals.illinois.edu/oai-pmh

oai:www.ideals.illinois.edu:2142/20984 2023-07-10 col_2142_5131 col_2142_14795 com_2142_5130 com_2142_14794 com_2142_14793 com_2142_8903

eng Switzer, Robert L. Post, David A. 2011-05-07T12:54:56Z 2011-05-07T12:54:56Z 10000-01-01 1992 Little is known about the amino acids present in the active site of the enzyme phosphoribosylpyrophosphate (PRPP) synthetase or the regulation of the structural gene (prs) in vivo. Site directed mutagenesis and characterization of mutant proteins were used to examine possible residues involved in catalysis. Initial studies of the transcriptional regulation of the prs gene were also conducted. The Salmonella typhimurium prsB mutant was reported to produce undetectable levels of PRPP synthetase activity (Pandey, N. K., and R. L. Switzer, J. Gen. Microbiol. 128: 1863-1871, 1982). It was shown that prsB was an allele of the prs gene, therefore it was renamed prs-100. The prs-100 mutation was the replacement of Arg-78 by Cys. The mutant PRPP synthetase was purified and determined to possess elevated Michaelis constants, a reduced maximal velocity (30% of wild type) and reduced sensitivity to the allosteric inhibition. It appears that the mutation alters the enzyme's kinetic properties through substantial structural alterations. Histidine 130 (His130) was proposed to have a role in divalent cation binding (Bower et al., J. Biol. Chem. 264: 10287-10291, 1989). To investigate this, His130 was replaced by glutamine, tyrosine, asparagine and aspartate by site directed mutagenesis. The mutant proteins were over-produced, purified and characterized. The mutant enzymes had altered Michaelis constants and maximal velocities. It was demonstrated that His130 was not involved in divalent cation binding, but was crucial for catalysis. The prs leader is 417 bp in S. typhimurium. The region between the prs coding region and an upstream gene (hemA) in S. typhimurium was cloned and sequenced. This region was shown to encode two ORFs of unknown function, which were transcribed in the same direction as the prs gene. Northern blots showed that the prs message is transcribed from two promoters, the first promoter (P$\sb1$) originating upstream of ORF 1, and expressing the prs gene in a tricistronic operon and a second promoter (P$\sb2$), located within the ORF 2 coding frame, which transcribes the prs gene only. Made available in DSpace on 2011-05-07T12:54:56Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9215870.pdf: 9933001 bytes, checksum: b7669e8c1c5350339dfb6d6d174c06e9 (MD5) Previous issue date: 1992 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:47:41Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:21:33-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission ETDs are only available to UIUC Users without author permission U of I Only AAI9215870 (UMI)AAI9215870 http://hdl.handle.net/2142/20984 Copyright 1992 Post, David A. Chemistry, Biochemistry Studies on the regulation in vivo and structure/function relationships of the enzyme 5-phosphoribosyl-alpha-1-pyrophosphate synthetase from Salmonella typhimurium text Biochemistry Biochemistry University of Illinois at Urbana-Champaign Dissertation Ph.D.