Masao Yamada

DNA analysis in hereditary dentatorubral-pallidoluysian atrophy Correlation between CAG repeat length and phenotypic variation and the molecular basis of anticipation

Article abstract-Hereditary dentatorubral-pallidoluysian atrophy (DRPLA) is an autosomal dominant neurodegenerative disease with variable clinical phenotypes. Progressive ataxia, choreoathetosis, and dementia are the main clinical features of adult-onset cases, whereas the main feature in juvenile-onset DRPLA is progressive myoclonus epilepsy. Earlier onset is apparent in successive generations (anticipation). The molecular abnormality underlying DRPLA is an expanded, unstable CAG trinucleotide repeat on chromosome 12p. We analyzed 71 DNA samples obtained from 12 Japanese DRPLA pedigrees that included 38 affected individuals. Normal alleles had 7 to 23 repeats, DRPLA alleles 53 to 88 repeats. DRPLA alleles also were detected in five asymptomatic family members. Patients with juvenile onset had significantly larger repeats than did those with adult onset, and there was a significant negative correlation between CAG repeat length and age at onset. In 80% of the paternal transmissions, there was an increase of more than five repeats, whereas all the maternal transmissions showed either a decrease or an increase of fewer than five repeats. There was a significant correlation between father-child differences in repeat length and differences in age at onset. The analysis of CAG repeat length is a reliable diagnostic test for DRPLA and is of value for the presymptomatic detection of individuals at risk. The expansion of CAG repeats is important in phenotypic variation and anticipation. In addition, the sex of the transmitting parent has a significant effect on the molecular mechanism of anticipation. NEUROLOGY 1995;45: 143-149

Dentatorubral Pallidoluysian Atrophy (DRPLA) Protein Is Cleaved by Caspase-3 during Apoptosis

Dentatorubral pallidoluysian atrophy (DRPLA) is an autosomal dominant neurodegenerative disorder. It is associated with an abnormal CAG repeat expansion resulting in formation of a protein with an elongated polyglutamine stretch. However, neither the physiological roles of the DRPLA gene product nor molecular mechanisms of its pathogenesis have yet been elucidated. Here we report that the DRPLA protein is cleaved at a site near the N terminus during apoptosis induced by VP-16, staurosporine, or glucocorticoid. Moreover, thein vitro translated DRPLA protein is cleaved by recombinant caspase-3, a member of the cysteine protease family, which is thought to be a main executioner of apoptosis. Using mutant DRPLA proteins, the cleavage site was identified as 106DSLDG110. The cleavage, however, was not modulated by the length of the polyglutamine stretch. These findings suggest that the DRPLA protein is one of the physiological substrates of caspase-3, and its cleavage may result in structural and biochemical alterations associated with apoptosis.

Nucleotide sequence of the asnA gene coding for asparagine synthetase of E.coli K-12

We have subcloned the asnA gene of E. coli K-12, a gene coding for asparagine synthetase, from a previously cloned 6 mega-dalton segment of E. coli chromosome containing the DNA replication origin, ori, and asnA. The complete nucleotide sequence of the asnA gene was determined: the region of the structural gene extends 990 base-pairs at nucleotide positions 1434-2423 (see Fig. 3), which codes for a polypeptide of 330 amino-acid residues with a molecular weight of 36,688 daltons. The nucleotide sequences of the promoter and the ribosome-binding site of the gene are also assigned. We discuss the properties of its polypeptide.