Induction of a new species of phenylalanine transfer RNA during lens cell differentiation

In vitro and in vivo models of Staphylococcus aureus endophthalmitis implicate specific nutrients in ocular infection

PURPOSE

To define global transcriptional responses of Staphylococcus aureus and its codY mutant (CodY is a transcription regulator of virulence and metabolic genes in response to branched-chain amino acids) when growing in bovine aqueous (AH) and vitreous humor (VH) in vitro, and to investigate the impact of codY deletion on S. aureus virulence in a novel murine anterior chamber (AC) infection model.

METHODS

For the in vitro model, differential transcriptomic gene expression of S. aureus and its codY mutant grown in chemically defined medium (CDM), AH, and VH was analyzed. Furthermore, the strains were inoculated into the AC of mice. Changes in bacterial growth, electroretinography and inflammation scores were monitored.

RESULTS

Bovine AH and VH provide sufficient nutrition for S. aureus growth in vitro. Transcriptome analysis identified 72 unique open reading frames differentially regulated ≥10-fold between CDM, AH, and VH. In the AC model, we found comparable growth of the codY mutant and wild type strains in vivo. Average inflammation scores and retinal function were significantly worse for codY mutant-infected eyes at 24 h post-infection.

CONCLUSION

Our in vitro bovine AH and VH models identified likely nutrient sources for S. aureus in the ocular milieu. The in vivo model suggests that control of branched-chain amino acid availability has therapeutic potential in limiting S. aureus endophthalmitis severity.

Rat lens beta-crystallins are internally duplicated and homologous to gamma-crystallins

The nucleotide sequence of two cloned rat lens beta-crystallin cDNAs pRL beta B3-2 and pRL beta B1-3 has been determined. pRL beta B3-2 contains the complete coding information for a beta-crystallin, designated beta B3, of 210 amino acid residues. pRL beta B1-3 is incomplete at its 5' end; the 5' codogenic information which is not present in this cDNA clone was deduced from the cloned gene. pRL beta B1-3 codes for a beta-crystallin polypeptide, designated beta B1, whose full length is 247 amino acid residues. Considerable sequence homology is noted between the amino- and carboxy-terminal halves of each protein. The two rat beta-crystallins show a substantial sequence homology with each other (60%) as well as with the published sequences of rat gamma-crystallin (37%) and bovine and murine beta-crystallins (55 and 45%). All these proteins have a two-domain structure which, like the bovine gamma II-crystallin, might be folded into four remarkably similar protein motifs. Our data further indicate that the beta-crystallins can be subdivided into two groups which are evolutionarily related. Both groups are, although more distantly, also related to the gamma-crystallins.

Tumor-specific tRNA modifications in mouse plasmacytomas and other tumors

RPC-5 chromatography has been used to analyze the aa-tRNA populations found in normal organs and in various tumors in experimental animals. The most extensively studied animal systems have been mineral-oil-induced mouse plasmacytomas and carcinogen-induced rat hepatomas. Certain aa-tRNA species appear to be tumor-specific, e.g., rat hepatoma phenylalanyl-tRNA1 and plasmacytoma asparaginyl-tRNAs2-4. In addition, one of the tumor-specific peaks of asparaginyl-tRNA can be found in normal livers of animals bearing plasmacytomas at a distant site. Many other significant quantitative and qualitative differences among histologically similar plasmacytomas and between normal tissues and plasmacytomas were observed in the chromatographic patterns of isoaccepting aa-tRNAs for 11 of 20 amino acids. Some of the qualitative differences in chromatographic patterns could be correlated with the tumorous nature of the tissue using computer analysis. The program utilized cluster analysis to compare the RPC-5 patterns of aa-tRNAs from 11 plasmacytomas and two normal tissues for each of the 20 amino acids. The variations in these chromatographic profiles are though to be caused by varying degrees of incomplete synthesis of some of the normally modified nucleosides in tRNAs.

Alterations in tRNA isoaccepting species during erythroid differentiation of the Friend leukemia cell

The chromatographic profiles of isoaccepting tRNAs were analyzed at five time points during the 96 hr, dimethylsulfoxide induced, erythroid-like differentiation of Friend leukemia cells. Sixty-four isoaccepting species of tRNA for 16 amino acids were resolved by RPC-5 chromatography. The relative amounts of tRNAphe, tRNAile, and tRNAval species were maintained by the cells during differentiation; whereas the relative amounts of some of the isoacceptor tRNAs for the other 13 amino acids changed significantly. Fluctuations in amounts of isoacceptors occurred between 36 and 72 hr after addition of dimethysulfoxide, corresponding to globin mRNA appearance and hemoglobin synthesis, respectively. In most cases, thepredominant tRNA isoacceptors of uninduced cells were retained throughout differentiation. Notable exceptions were tRNA species for threonine, proline, and methionine. Some of the isoacceptors occurring in relatively smaller amounts were not expressed at all times. These changes possibly reflect the cell's functional adaptation of tRNA in differentiation for hemoglobin synthesis.

Abundance of tRNAPhe lacking the peroxy Y-base in mouse neuroblastoma

Affinity chromatography on anti-Y (Y is a tricyclic imidazopurine to which is attached a complex four-carbon side chain) antibody immobilized to Sepharose was used to determine the proportion of rat liver tRNAPhe species containing the peroxy Y-nucleoside. Unfractionated Unfractionated mammalian tRNA was aminoacylated with labeled phenylalanine. The phenylalanyl-tRNA was then chemically acetylated to yield N-acetylphenylalanyl-tRNA. When this preparation was applied to the antibody column, between 6-10% of the radioactivity was not bound to the column, indicating a deficiency of peroxy Y-nuceloside in a minor isoaccepting tRNAPhe species. In contrast to normal tissues (including embryonic tissue), about 85% of the tRNAPhe from mouse neuroblastoma C-1300 or N-18 tumors lack the peroxy Y-base, a property which is not affected by tumor age. Rat liver labeled N-acetylphenylalanyl-tRNA preparations were resolved on Plaskon chromatography (RPC-5) into two minor peaks closely followed by a mojor component. A high proportion of the two minor tRNAPhe species was unable to bind to anti-Y antibodies. Upon mild acid treatment, the minor and major tRNAPhe species eluted simultaneously from Plaskon columns, at a much reduced salt concentration. These results would indicate that the two minor tRNAPhe species from rat liver as well as the major component contain a tricyclic imidazopurine base that differs from each other in its side chain. About 85% of the N-acetylphenylalanyl-tRNA from neuroblastoma was resolved by Plaskon chromatography as an early eluting peak. The position of this major neuroblastoma tRNAPhe species was not altered by mild acid treatment, and its elution position from the column almost coincides with that of acid-treated normal rat liver tRNAPhe. The latter results would suggest that most of the tRNAPhe chains from neuroblastoma lack the tricyclic imidazopurine of normal rat liver tRNAPhe, but are very close if not identical in primary nucleotide sequence.