Analysis of the upstream region of the Escherichia coli rnd gene encoding RNase D. Evidence for translational regulation of a putative tRNA processing enzyme

The upstream region of the Escherichia coli rnd gene has been analyzed. A single promoter and transcription start site were identified in the 170-nucleotide upstream region of the clone based on deletion analysis, nuclease S1 mapping, primer extension, and quantitative dot-blots. The start site of transcription is 70 nucleotides upstream of the UUG initiation codon of the RNase D coding region. Between the RNA initiation site and the coding region is a GC-rich hairpin structure followed by 8 T residues that looks like a rho-independent transcription terminator. Surprisingly, deletion of the hairpin structure elevates rnd mRNA levels only slightly (less than 2-fold), but it dramatically decreases RNase D expression (greater than 95%), measured both by activity and immunoblotting. No evidence for an effect on mRNA stability or processing was observed. The uncommon UUG translation initiation codon was converted to AUG by site-directed mutagenesis. This alteration led to an 11-fold elevation of RNase D expression in single-copy plasmids. These data indicate that RNase D expression is negatively regulated at the translational level by the initiation codon, and that an upstream structure (or sequence) also influences translation of this gene.

[Effects of microiontophoretically applied flurazepam on the respiratory units in the region of the nucleus parabrachialis of the rabbit]

Experiments were carried out on 36 urethane-chloralose aneasthesized, paralyzed, vagotomized and artificially ventilated rabbits. Five-barrel glass micropipettes were used to record unit discharges and to apply flurazepam iontophoretically in the region of the nucleus parabrachialis. Inspiratory units (IUs), expiratory units (EUs), phase-spanning units (I-EUs and E-IUs) and non-respiratory units (NRUs) were observed. 26 (55.3%) out of 47 IUs, 17 (94.4%) out of 18 EUs, 11 (91.7%) out of 12 I-EUs, 2 (18.1%) out of 11 E-IUs and 43 (60.6%) out of 71 NRUs were depressed by flurazepam. The depressant ratio of EUs and I-EUs was statistically different from that of IUs and E-IUs respectively. In flurazepam sensitive 5 IUs and 2 EUs, the depressant effect could not be antagonized by GABA-A receptor antagonist bicuculline. In 10 flurazepam sensitive NRUs, there were 6 (60%) units whose depressant effect of flurazepam could be antagonized by bicuculline. In addition, the effects of acetylcholine (ACh) on the respiratory units and NRUs were examined, 15 (75%) out of 20 IUs were excited and the remaining units were not influenced. The effects of ACh on the EUs, I-EUs and E-IUs were variable, but the effects of ACh on the NRUs were mainly excitatory. In 5 IUs and 1 phase-spanning respiratory units, the depressant effect of flurazepam could not be antagonized by ACh. The results showed that flurazepam mainly depressed the EUs and I-EUs in the region of nucleus parabrachialis, thus interfering with the normal phase transition between the inspiratory and expiratory phase and reducing the respiratory rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Transfer RNA is a substrate for RNase D in vivo

RNase D is a 3'-exonuclease whose in vitro specificity has suggested a role in tRNA processing. However, since mutant Escherichia coli strains devoid of RNase D display a normal phenotype, it has not been possible to ascertain the enzyme's function or even to determine which RNA is its substrate in vivo. Here we show that transformation of strains devoid of tRNA nucleotidyltransferase with a multicopy plasmid carrying the rnd+ gene leads to extremely slow growth due to elevated levels of RNase D activity. Analysis of such a slow-growing strain revealed that less tRNA is present in the cell and that the tRNA that could be recovered is substantially damaged. These studies demonstrate that RNase D can act at the 3' terminus of tRNA in vivo, and they support the conclusion that RNase D participates in tRNA metabolism.

Escherichia coli RNase D: sequencing of the rnd structural gene and purification of the overexpressed protein

We have determined the nucleotide sequence of a 1.4-kb-pair fragment of the E. coli chromosome that carries the complete rnd gene encoding RNase D, a putative tRNA processing enzyme. The coding region of rnd extends for a total of 1128 nucleotides beginning at an initiator UUG codon and terminating at a UAA codon, and encodes a 375-amino acid polypeptide of 42,679 daltons, consistent with the known size of RNase D. A rapid purification procedure was developed for isolation of RNase D from strains overexpressing the enzyme. The N-terminal sequence and the amino acid composition of the homogenous protein were in excellent agreement with those derived from the sequence of the rnd gene.

Laser-induced multiphoton fluorescence of hemoglobin

Hemoglobin (Hb) and other samples were irradiated by the 1064 nm nanosecond pulses of an Nd:YAG laser. At room temperature, we observed two red fluorescence bands, which resulted from the absorption of two 1064 nm photons in Hb, and measured the fluorescence emission spectra in the red spectral region for Hb and hematoporphyrin derivative. A red shift of the wavelength and a mirror image in the intensity of fluorescence emissions by two-photon excitation were observed. It is shown that the fluorescence of Hb originates from the heme group. In addition, we also observed fluorescence emission at 392 nm for Hb, which may be from its tryptophan groups.

Cloning, characterization, and effects of overexpression of the Escherichia coli rnd gene encoding RNase D

RNase D is a 3'-exoribonuclease whose in vitro specificity has suggested that it is involved in the processing of tRNA precursors. Its in vivo role has remained unclear, however, because mutant cells devoid of the enzyme display no defect in growth or tRNA processing. To learn more about the structure and function of RNase D, we cloned the Escherichia coli rnd gene, which is thought to code for this enzyme. The rnd gene was isolated from a cosmid library based on elevated RNase D activity and was subcloned as a 1.4-kilobase-pair fragment in pUC18. Maxicell analysis of the cloned fragment revealed that a single protein of approximately 40 kilodaltons, which is the size of RNase D, was synthesized. The rnd gene is present as a single copy on the E. coli chromosome and is totally absent in a deletion mutant. Cells that harbored the cloned rnd gene displayed RNase D activity that was elevated as much as 20-fold over that of the wild type. As growth of the culture progressed, however, RNase D specific activity declined dramatically, together with a similar decrease in plasmid copy number. In contrast, no decrease in copy number was observed with an inactive rnd gene. Placement of the rnd gene downstream from the lac promoter led to inducible RNase D overexpression and concomitantly slowed cell growth. These findings support the idea that rnd is the structural gene for RNase D and indicate that elevated RNase D activity is deleterious to E. coli.

Fluorescence of proteins induced by two-photon absorption

At room temperature, the UV fluorescence of trypsin, thyroglobulin, hemoglobin and albumin are observed; these molecules undergo two-photon absorption when they are excited with the radiation of a frequency-duplicated Q-switched Nd:YAG laser. It is shown that the fluorescence of these proteins comes from the tryptophan residues and that it has a red shift of about 20 nm relative to the one-photon fluorescence. We suggest that the weak emission from tyrosine arises from the forbidden two-photon transition. The influence of concentration on the fluorescence of hemoglobin and tryptophan is discussed. The two-photon absorption cross-sections are estimated.