β-Amyloid Protein Precursor and τ mRNA Levels Versus β-Amyloid Plaque and Neurofibrillary Tangles in the Aged Human Brain

Abstract: To learn whether or not the levels of β-amyloid protein precursor (APP) and τ mRNAs are related to the formation of β-amyloid and neurofibrillary tangles, we quantified these mRNA levels in three cortical regions of 38 aged human brains, which were examined immunocyto-chemically for β-amyloid and tangles. Marked individual variabilities were noted in APP and τ mRNA levels among elderly individuals. The mean APP mRNA level was slightly reduced in the β-amyloid plaque (++) group, but not in the plaque (+) group, compared to the plaque (−) group. Some brains in the plaque (−) group showed increased APP expression, the extent of which was not seen in the plaque (+)or(++) group. The differences in the mean τ mRNA levels were not statistically significant among the tangle (−), (+), and (++) groups. These results show that β-protein and τ deposition do not accompany increased expression of the APP and τ genes, respectively, and thus suggest that factors other than gene expression may be at work in the progression of β-amyloid and/or tangle formation in the aged human brain.     

An alternative non-tyrosine protein kinase product of the c-src gene in chicken skeletal muscle.

While the c-src locus is expressed as a 4.0-kilobase (kb) mRNA coding for pp60c-src in various chicken tissues, including embryonic muscle, it is expressed as a novel 3.0-kb mRNA in adult skeletal muscle. We have analyzed the primary structure of this alternatively transcribed and spliced c-src mRNA. The sequence revealed three open reading frames, with the previously defined c-src exons 1 through 5 or 6 comprising the third, on the 3' untranslated region of this 3-kb mRNA. The exons coding for the tyrosine kinase domain of pp60c-src were excluded. On the 5' side, 2 kb of sequence upstream from the previously defined exon 1 of the c-src gene was included in this mRNA. The start site for the 3-kb mRNA probably lies downstream of that for the 4-kb mRNA. The first reading frame of the 3.0-kb mRNA, called sur (for src upstream region), encoded a 24-kilodalton (kDa) protein product rich in cysteine and proline residues. In vitro analysis indicated that the 24-kDa sur protein was membrane associated. Antibodies to sur protein detected in vivo a 24-kDa muscle-specific protein which was developmentally regulated and corresponded to the switch from the 4-kb to the 3-kb c-src mRNA. A striking kinetic pattern of appearance of sur protein and disappearance of pp60c-src suggests that the expression of these two proteins is inversely related.     

Analysis of Cre1 binding sites in the Trichoderma reesei cbh1 upstream region

Abstract A 1.5-kb XbaI-SacII fragment containing the upstream region of the Trichoderma reesei cellobiohydrolase I gene ( cbh1 ) has been sequenced. The 1.5-kb fragment contains eight 6-bp sites having an identical or similar sequence to the consensus sequence for binding a catabolite repressor, Aspergillus nidulans CreA. Results of binding assays with the maltose-binding protein: :Cre1(10–131) fusion protein (Cre1 is a catabolite repressor of T. reesei ) and the cbhI upstream region revealed that a 504-bp XbaI-NspV fragment (nucleotide position − 1496 to − 993) bearing three 6-bp sites, Al, A2, and A3, and a 356-bp NspV-MunI fragment (nucleotide position −994 to −639) bearing three 6-bp sites, B1, B2, and B3, were shifted in the electrophoretic mobility shift assay. DNase I footprinting experiments showed that the 6-bp sites A2, B1, B2, and B3 were protected from DNase I digestion.     

Human acyl-CoA:cholesterol acyltransferase-1 (ACAT-1) gene organization and evidence that the 4.3-kilobase ACAT-1 mRNA is produced from two different chromosomes

Acyl-CoA:cholesterol acyltransferase (ACAT) plays important roles in cellular cholesterol homeostasis. Four human ACAT-1 mRNAs (7.0, 4.3, 3.6, and 2.8 kilobases (kb)) share the same short 5'-untranslated region (exon 1) and coding sequence (exons 2-15). The 4.3-kb mRNA contains an additional 5'-untranslated region (1289 nucleotides in length; exons Xa and Xb) immediately upstream from the exon 1 sequence. One ACAT-1 genomic DNA insert covers exons 1-16 and a promoter (the P1 promoter). A separate insert covers exon Xa (1277 base pairs) and a different promoter (the P7 promoter). Gene mapping shows that exons 1-16 and the P1 promoter sequences are located in chromosome 1, while exon Xa and the P7 promoter sequence are located in chromosome 7. RNase protection assays demonstrate three different protected fragments, corresponding to the 4.3-kb mRNA and the two other mRNAs transcribed from the two promoters. These results are consistent with the interpretation that the 4.3-kb mRNA is produced from two different chromosomes, by a novel RNA recombination mechanism involving trans-splicing of two discontinuous precursor RNAs.