Accumulation of photosynthesis gene transcripts in response to sodium chloride by salt-tolerant alfalfa cells

A cell line from diploid alfalfa (Medicago sativa L.), HG2-N1, which is stably tolerant to 1% (0.171 M) NaCl in the medium and noticeably more green than the parent line (HG2), was investigated to determine if increased chlorophyll accumulation was related to chloroplast development toward greater photosynthetic activity and increases in chloroplast-gene expression in this cell line. The ctDNA (chloroplast-DNA) copy number in HG2-N1 was found to be increased by 50% from that of the salt-sensitive parent HG2 line. RNA accumulation, as detected by hybridization to a nuclear actin gene, appeared comparable in HG2 and HG2-N1. In contrast, mRNA levels of the plastid-encoded psbA gene were increased in the salt-tolerant HG2-N1 grown on normal medium. The mRNA levels of HG2-N1 were further increased in response to added NaCl in the medium. The mRNA levels from other chloroplast genes necessary for photosynthesis (psbD, psaB, atpB, rbcL), as well as from several nuclear genes (pCab4, pCab1, rbcS) encoding polypeptides participating in photosynthesis, also increased in the salt-tolerant HG2-N1 when it was grown in the presence of NaCl whereas actin-mRNA and chloroplast-rRNA levels remained comparable under growth conditions ± NaCl. Several independently isolated salt-tolerant cell lines showed a similar response to salt, as monitored by accumulation of rbcL mRNA, indicating that transcript accumulation for photosynthesis genes is correlated with the salt response in these salt-tolerant alfalfa cell lines.

Cloning of rat "prion-related protein" cDNA

Rat prion-related protein (PrP) cDNA has been cloned and sequenced. Comparison of this cDNA with those from human, hamster, and mouse indicates extremely high conservation (about 95%). The deduced partial rat PrP possesses: (a) a highly conserved region composed of repetitive sequences in what is presumably an extracellular domain, (b) a hydrophobic transmembrane domain, (c) a highly charged region which should stop membrane transfer, (d) a substantial cytoplasmic domain (which contains all of the nonconservative substitutions and a high proportion of conservative substitutions), and (e) a hydrophobic C-terminus. Dot and Northern blot analyses suggest a limited expression of PrP in rat tissues and indicate that PrP expression is decreased in the brain during the acute phase response systemically. Our results lend support to the notion that PrP is a highly conserved, normal cellular membrane protein of essential (although unknown) biologic function, which may be deposited in fibrillar amyloid form as a result of abnormal processing.

Hepatocarcinogen-induced alterations in nuclear RNA compartmentation

Prelabeled rat liver nuclei were purified, detergent-rinsed to remove cytoplasmic RNA contaminants and incubated in two in vitro RNA transport assays. Appropriate compartmentation of nuclear RNA sequences was maintained in an assay containing polyvinylpyrrolidone (PVP), which prevents nuclear swelling in aqueous media. Under these conditions, poly(A)+ RNA released in the presence of PVP (and ATP) was significantly more active in directing in vitro protein synthesis than poly(A)+ RNA released in the absence of either additive. Further, the excised fifth intron of alpha 1-acid glycoprotein remained nucleus-restricted, while release of poly(A)+ processing catabolites occurred in the absence of PVP. The appropriate compartmentation of nuclear sequences was lost following treatment of rats with the hepatocarcinogen thioacetamide, paralleling the in vivo situation. This assay should prove useful for subsequent studies on nucleocytoplasmic RNA transport in vitro, in particular for investigations relating to the altered RNA transport associated with the initiation of carcinogenesis.

Cytoplasmic RNA complementary to pre-albumin intron V

We have detected an RNA species, containing sequences complementary to pre-albumin intron V in poly(A)+ RNA from rat liver cytoplasm (but not in nuclear RNA). Its relative abundance roughly parallels that of mature albumin mRNA, when comparing control with acute phase preparations.

Dichlorobenzimidazole-riboside inhibition of nuclear RNA accumulation initiated with gamma-thio analogues of ATP and GTP

The gamma-thio analogues of ATP and GTP, ATP[S] and GTP[S], have been used as affinity probes to measure RNA synthesis initiated in vitro in L cell nuclei. 5,6-Dichlororibofuranosylbenzimidazole was found to inhibit total RNA synthesis in vitro and the amount bound by mercury-affinity chromatography. Initiation in vitro was also shown by [35S]ATP[S] and [35S]GTP[S] incorporation in RNA molecules with a larger size distribution. Although 66% of RNA molecules labeled with [35S]GTP[S] and 74% of those labeled with [35S]ATP[S] were 3-12 S n size, the remainder of the label was recovered in RNA molecules larger than 12 S and a significant portion in RNA larger tha 18 S. The specificity of the initiation process seems to be indicated by the finding of molecules of the size of pre-tRNA on gel electrophoresis which were labeled with [35S]GTP[S] but not [35S]ATP[S] under our experimental conditions. 5,6-Dichlororibofuranosylbenzimidazole severely inhibited the incorporation of [35S]GTP[S] and [35S]AT[[S] by all size classes, indicating that it can decrease accumulation of RNA initiated in vitro in the L cell nuclear system.

Nuclear ligation of RNA 5'-OH kinase products in tRNA

Mouse L-cell nuclei incorporate gamma-32P from ATP in vitro predominantly in 5'-monophosphoryl termini and internal phosphodiester bonds with a nonrandom nearest-neighbor distribution. In the presence of 1 microgram of alpha-amanitin per ml the gamma-32P showed a time-dependent appearance in RNA bands which migrated with mature tRNA species but not with pre-tRNA and 5S RNA. The gamma-32P was found in internal phosphodiester bonds as shown by alkaline phosphatase resistance and was identified in 3'-monophosphates after RNase T2, T1, and A digestion. The specificity of this incorporation was indicated by a limited number of labeled oligonucleotides from a T1 digest and identification of 70 to 80% of the 32P label as Cp on complete digestion of the eluted tRNA band. We also observed transiently [gamma-32P]ATP-labeled RNA bands (in 5'-monophosphate positions) that were 32 to 45 nucleotides long. The results presented suggest splicing of several mouse L-cell tRNA species in isolated nuclei which involve the RNA 5'-OH kinase products as intermediates.