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SummaryThe petunia mitochondrial fused gene (pcf), which is associated with cytoplasmic male sterility (CMS), is composed of sequences derived from atp9, coxll, and an unidentified reading frame termed urfS. Pcf transcripts are modified by editing at 11 sites. Codon usage and nearest neighbor analysis suggest that the urfS region is not derived originally from a plant mitochondrial coding region. Although the gene contains an open reading frame coding for a 43 kDa protein, a 25 kDa gene product has previously been identified (Nivison and Hanson, 1989). N-terminal sequencing revealed that the 25 kDa protein is encoded within the urfS portion of pcf and that its actual molecular mass is 19.5 kDa. Through pulsechase labeling of protein in isolated mitochondria, the 25 kDa protein was found to be processed from a 43 kDa precursor protein representing the entire pcf gene sequence. Antibodies to synthetic peptides encoded by the atp9 and coxll portions of pcf recognized petunia ATP9 or COXll but no other mitochondrial proteins on immunoblots. Controlled proteolysis experiments showed that both the 43 kDa precursor and the 25 kDa protein are soluble or loosely associated with membranes. Thus, the 25 kDa protein appears to be the only pcf-encoded protein that accumulates in mitochondria.

Paradichlorobenzene (PDB) is a common household deodorant and pesticide found in room deodorizers, toilet bowl fresheners, and some mothballs. Although human exposure to the compound is generally limited and harmless, PDB in larger doses can produce neurotoxic effects, including a chemical "high" similar to that seen with inhalants such as toluene. Although rare, frank addiction to PDB has been reported, and, in such cases, has been associated with gait ataxia, tremor, dysarthria, limb weakness, and bradyphrenia, in various combinations. In such cases, the adverse neurologic consequences have been presumed to result from a direct toxic effect of this small, organic molecule. We report a case of chronic mothball ingestion where profound encephalopathy with cognitive, pyramidal, extrapyramidal, and cerebellar features appears to have been largely the result of PDB withdrawal, rather than direct toxicity. This case raises important questions about the mechanism of PDB neurotoxicity and possible treatment options for PDB-addicted patients. We propose that in cases with clear clinical deterioration after abstinence, readministration and gradual taper of PDB might be considered a therapeutic option.

Objective: To identify the proportion of patients in a large idiopathic normal pressure hydrocephalus (INPH) cohort with large head circumference (HC) who presumably have congenital hydrocephalus that has not become clinically apparent until late in life. Methods: HC was measured in 158 patients diagnosed with communicating INPH and assigned to HC centile range adjusted for height and sex. The proportion of patients with INPH and HC above the 97th, 90th or 50th centiles was compared with the proportion expected in a normal population. Results: The proportion of patients with HC .90th centile was significantly larger than would be expected in a normal distribution (19.6% vs 10%, p = 0.0001), as was the proportion of patients with HC .97th centile (8.9% vs 3%, p = 0.0001). The relative association between INPH and HC .97th centile was nearly tripled (relative association 2.95; CI 1.36 to 6.41), but the relative association between INPH and HC .50th centile was not significantly higher than predicted (relative association 1.13; CI 0.95 to 1.34). Conclusion: A significantly larger proportion of elderly adults with INPH have a HC greater than the 90th or 97th centile than predicted by population norms, supporting the concept that compensated congenital hydrocephalus that does not become symptomatic until late in life is one aetiology of INPH, but is not responsible for all INPH. The mechanism that leads to the development of INPH in most patients remains elusive.

Several different RNA processing events can occur during the maturation of a protein-coding plant mitochondrial transcript. These events distinguish plant mitochondria from their mammalian counterparts and include RNA editing, cis-splicing and, as we will describe here, trans-splicing.RNA editing has been shown to occur in many, if not all, plant mitochondrial protein-coding genes; specific cytidines in the DNA sequence are altered in the RNA and appear as thymidines in the cDNAs that are isolated from these genes (Covello and Gray 1989;Gualberto et al. 1989;Hiesel et al. 1989). This is consistent with a process that alters cytidine into uridine residues, although uridine in place of cytidine in edited RNAs has not been directly demonstrated. The extent of RNA editing varies from gene to gene. et al. 1986). The first of these two exons was also described in tobacco and maize (Bland et al. 1986). Two additional nadl exons, predicted to encode the carboxy-terminal portion of nadl, were recently reported in the broad bean mitochondrial genome. Two group II intron-like domains were found upstream of the first of these two exons.Within the group II intron that separates these broad bean nadl exons, a maturase-like gene (mat-r) was found. The protein sequence predicted from this gene is similiar to the maturases encoded within fungal mitochondrial introns (Wahleithner et al. 1990). As yet, it is not known whether the plant mat-r sequences actually specify a protein with maturase activity.We commenced to clone the P. hybrida nadl exons using probes from both watermelon and broad bean. In addition to the exons described above, we cloned and mapped an exon that encodes the amino-terminal portion of NAD1 with the use of a probe from the equivalent wheat exon (Chapdelaine and Bonen 1991). A complete restriction map of the Petunia mitochondrial ge-

The rps12 gene transcripts encoding mitochondrial ribosomal protein S12 are partially edited in petunia mitochondria. Different petunia lines were found vary in the extent of rps12 transcript editing. To test whether multiple forms of RPS12 proteins are produced in petunia mitochondria as a result of partial editing, we probed mitochondrial proteins with specific antibodies against edited and unedited forms of a 13-amino-acid RPS12 peptide spanning two amino acids affected by RNA editing. Both antibodies reacted with mitochondrial proteins at the expected size for RPS12 proteins. The amounts of unedited RPS12 protein in different petunia lines correlate with the abundance of unedited transcripts in these plants. Unedited rps12 translation products are also detected in other plant species, indicating that polymorphism in mitochondrial rps12 expression is widespread. Moreover, we show that RPS12 proteins recognized by both edited-specific and unedited-specific antibodies are present in a petunia mitochondrial ribosome fraction. These results demonstrate that partially edited transcripts can be translated and that the protein product can accumulate to detectable levels. Therefore, genes exhibiting incompletely edited transcripts can encode more than one gene product in plant mitochondria.

The neurologist is in a unique position to differentiate NPH from alternative diagnoses, to suggest management strategies for patients with concomitant NPH and another neurologic disorder, and to participate in longitudinal management of NPH.

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