Human mitochondrial RNA turnover caught in flagranti: involvement of hSuv3p helicase in RNA surveillance

The mechanism of human mitochondrial RNA turnover and surveillance is still a matter of debate. We have obtained a cellular model for studying the role of hSuv3p helicase in human mitochondria. Expression of a dominant-negative mutant of the hSUV3 gene which encodes a protein with no ATPase or helicase activity results in perturbations of mtRNA metabolism and enables to study the processing and degradation intermediates which otherwise are difficult to detect because of their short half-lives. The hSuv3p activity was found to be necessary in the regulation of stability of mature, properly formed mRNAs and for removal of the noncoding processing intermediates transcribed from both H and L-strands, including mirror RNAs which represent antisense RNAs transcribed from the opposite DNA strand. Lack of hSuv3p function also resulted in accumulation of aberrant RNA species, molecules with extended poly(A) tails and degradation intermediates truncated predominantly at their 3′-ends. Moreover, we present data indicating that hSuv3p co-purifies with PNPase; this may suggest participation of both proteins in mtRNA metabolism

Estimation and comparison of the contents of blood group B antigens in selected human tissues by microphotometric quantification of Griffonia simplicifolia agglutinin 1-B, staining with or without prior a-galactosidase digestion

Griffonia simplicifolia agglutinin 1-B4 (GSAI-B4) has broader specificity for B antigen variants and can recognize the antigens in a wide variety of human tissues. Thus, the concentration range of GSAIB4 required for staining and the susceptibility of staining to a-galactosidase digestion is presumed to correlate well with the density of B antigens in tissue sections. By microphotometric quantification of staining intensity at different concentrations of GSAI-B4 with or without agalactosidase digestion, concentration of B antigens in selected tissues was evaluated and compared. Based on the present results and the previous ones of direct measurement of galactose of B antigens in sublingual glands and red blood cells (Ito et al., 1993), the order of concentration of B antigens in tissues examined was estimated as follows; mucous cells of sublingual glands from German nonsecretors < red blood cells and vascular endothelial cells (=2.7x10-3nmole/cm2), thyroid papillary carcinomas and Hassall's corpuscles from nonsecretors < mucous cells of sublingual gland from Japanese nonsecretors < pancreatic acinar cells from both secretor and nonsecretors, Hassall's corpuscles and kidney collecting tubules form secretors < mucous cells of sublingual gland from secretors (>8.5-11.7 nmole/cm2) and mucous cells of Brunner 'S gland from nonsecretors < mucous cells of Brunner's gland from secretors. From the above estimation, it is apparent that the expression of B antigen in Brumer's gland is partly dependent on the secretor status of individuals and that Japanese nonsecretors secrete substantial amounts of B antigens from sublingual gland while German nonsecretors do not. The present results also revealed an unexpected staining behavior of GSAI-B4 in some tissues, i.e. in mucous cells of sublingual glands and collecting tubules of kidney from secretors, staining olrprint reguests to: Nobuaki Ito, Ph.D., Department of Legal Medicine, Nara Medical University, Kashihara Nara 834, Japan intensity was markedly depressed at higher concentration of the lectin and this depression was recovered by prior a-galactosidase digestion. In addition, the present method was successfully applied for the estimation of the content of B antigens neoexpressed in thyroid papillary carcinomas, showing that the content of B antigen had a similar leve1 to that of red blood cells and vascular endothelial cells