Intron-exon Structure of Ubiquitin C-terminal Hydrolase-L1

Parkinson's disease (PD) is a common neurodegen- erative movement disorder characterized by tremor, bradykinesia, postural instability and muscular rigidity. Neuropathologically, it is defined by cell loss in the sub- stantia nigra associated with the presence of intraneu- ronal inclusions called Lewy bodies (LB) and processes engorged with proteinaceous material, the Lewy neurites. The recent identification of mutations in the a-synuclein gene in some familial forms of PD 3'6 and the demon- stration of accumulation of the protein in Lewy bod- ies and Lewy neurites7 suggest that abnormal protein aggregation may cause the disease. In addition to a- synuclein, LBs contain ubiquitin, proteasomal subunits 2 and ubiquitin C-terminal hydrolase-Ll,5 pointing to a po- tential participation of the ubiquitin-proteasome degra- dation pathway in the onset of the disease. We con- firmed this hypothesis by identifying a missense mutation in the ubiquitin C-terminal hydrolase LI (UCH-L1) gene in a German family with an autosomal dominant form of PD.4 UCH-L1 is highly specific for neurons and cells of the diffuse neuroendocrine system, and represents 1% to 5% of the total brain protein extract. 8 Northern blot analy- sis reveals a 1.3-kb brain-specific transcript broadly rep- resented in all areas of the brain tested, particularly in the substantia nigra (Fig. 1). Enzymes belonging to the ubiquitin C-terminal hydrolases family can re- move small amides and esters at the carboxyl terminus of ubiquitin and have been shown to hydrolyze peptides and small proteins similarly (reviewed in 9). They con- tribute to the pool of free monomeric ubiquitin molecules by hydrolysing the ubiquitin polymeric proprotein or ubiquitin-ribosomal fusion proteins during the matura- tion of the ribosome.9 The Ile93Met mutation observed in 2 PD patients4 causes a partial loss of catalytic activity of the UCH-L1 enzyme which could induce aberrations in the degradation pathway and lead to aggregation of proteins. To permit the rapid screening for mutations and assess the UCH-L1 role in PD, we have established specific amplification assays for all of its coding exons.