Organization and Regulation of the Qa (Quinic Acid) Genes in Neurospora crassa and Other Fungi

Abstract

In Neurospora crassa, five structural genes and two regulatory genes control the use of quinic acid as a carbon source. All seven genes are tightly linked to form the qa gene cluster. The entire cluster, which has been cloned and sequenced, occupies a continuous DNA segment of 17.3 kb. Three pairs of genes are divergently transcribed, including the two regulatory genes that are located at one end of the cluster and that encode an activator (qa-1F) and a repressor (qa-1S). Three of the structural genes (qa-2, qa-3, and qa-4) encode inducible enzymes that catalyze the catabolism of quinic acid. One structural gene (qa-y) encodes a quinate permease; the function of the fifth gene (qa-x) is still unclear. Present genetic and molecular evidence indicates that the qa activator and repressor proteins and the inducer quinic acid interact to control expression at the transcriptional level of all the qa genes. The activator, the product of the autoregulated qa-1F gene, binds to symmetrical 16 base pair upstream activating sequences located one or more times 5' to each of the qa genes. A conserved 28 amino acid sequence containing a six cysteine zinc binding motif located in the amino terminal region of the activator has been directly implicated in DNA binding. Evidence for other functional domains in the activator and repressor proteins are discussed. Indirect evidence suggests that the repressor is not a DNA-binding protein but forms an inactive complex with the activator in the absence of the inducer.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular cloning and characterization of the aroD gene encoding 3-dehydroquinase from Salmonella typhi

“…typhi aroD with that derived for another gene encoding a protein involved in aromatic amino acid biosynthesis from S. typhi, the aroC gene (Charles et al, 1990), shows a high degree of similarity in the choice of which codons are most frequently used. The pattern is consistent for those genes that are poorly expressed in E. coli (Grantham et al, 1981). There are some minor differences in codon preference, e.g.…”

“…nidulans and N . crassa (Giles et al, 1985). In A. nidulans the quinate-inducible 3-dehydroquinase is the product of the QuTE gene and has an M , of 16505.…”

QIP, a putative exonuclease, interacts with the Neurospora Argonaute protein and facilitates conversion of duplex siRNA into single strands

“…He, P. Cheng, Q. Liu, and Y. Liu, in prep.). The inverted repeats of al-1 are controlled by the quinic acid (QA)-inducible (qa-2) promoter (Giles et al 1985), so the addition of QA in the medium will lead to the production of dsRNA and inhibition of carotenoid biosynthesis. As shown in Figure 1A, when the siRNA was analyzed by a denaturing gel, addition of QA resulted in al-1-specific siRNA production in both strains, but the level of siRNA was significantly higher in the qde-2 rip strain than that in the wild-type strain.…”

The QUTA activator and QUTR repressor proteins of Aspergillus nidulans interact to regulate transcription of the quinate utilization pathway genes

“…This is unlikely, as the gene encoding this second putative repressor should have been identified in the mutant screens that were originally employed to generate and analyse the qat and qa mutants of A. nidalans and N . crassa (Grant e t al.,1988;Giles et al, 1985). Furthermore, the QUTR and QA-1S proteins have no recognized motifs capable of DNA binding Huiet & Giles, 1986) and are therefore unlikely to act by binding to promoter regions to inhibit transcription, or to act as DNA-dependent activators of the transcription of a second repressor gene.…”