The acu loci have been mapped and are widely distributed over the genome of A . nidulans. Close linkage has only been found between acuA and acuD (less than 1 0 0 recombination). There is no evidence for any pleiotropic mutation in that region affecting the expression of both these genes.Poor induction of the enzymes of the glyoxylate cycle, isocitrate lyase and malate synthase in mutants lacking acetyl-CoA synthase, and also in the other two classes of fluoroacetate-resistant mutants, indicates that the inducer, acetate, may be metabolized to a true metabolic inducer, perhaps acetyl-CoA, to effect formation of the enzymes. There is no evidence of any other class of pleiotropic recessive ucu mutations affecting the expression of the ucuD and acuE genes, which are therefore thought to be subject to negative rather than positive control.

We have isolated a novel gene, DIR1, from L132 cells that is transiently repressed after exposure to low radiation doses and has a potential role in induced radioresistance. Molecular and cellular characterization of this gene reveals that it is unique but has similarities to a family of heat-shock-related proteins known as immunophilins. These have been implicated in various cellular functions including general stress responses and control of the cell cycle. Antisense strategies have demonstrated that the DIR1 gene also appears to have some involvement in the control of the cell cycle. Furthermore, there appears be a potential role for this gene product in the phenomenon of induced radioresistance through a mechanism that increases the rate of DNA repair in cells exposed to X rays and subsequently increases the cells' resistance to radiation. This is the first description of an immunophilin-like gene that has a possible role in adaptive/inducible responses to X rays in mammalian cells.

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The predicted amino acid sequence of the product of the acetate-inducible mu-8 gene of Neurospora crassa, previously of unknown function, has close homology to the recently published sequence of Sacchuomyces cereuisiae acetyl-CoA hydrolase. An acu-8 mutant strain, previously characterized as acetate non-utilizing, shows strong growth-inhibition by acetate, but will use it as carbon source at low concentrations. The mutant was shown to be deficient in acetyl-CoA hydrolase and to accumulate acetyl-CoA when supplied with acetate. As in Saccharomyces, the Neurospora enzyme is acetate-inducible.

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