Biomedical subjects

A L Bricker

Publications and source records attributed to A L Bricker.

4 recordsLinked to original sources

PubMed2000

An evolutionarily conserved RNA stem-loop functions as a sensor that directs feedback regulation of RNase E gene expression.

RNase E is a key regulatory enzyme that controls the principal pathway for mRNA degradation in Escherichia coli. The cellular concentration of this endonuclease is governed by a feedback mechanism in which RNase E tightly regulates its own synthesis. Autoregulation is mediated in cis by the 361-nucleotide 5' untranslated region (UTR) of rne (RNase E) mRNA. Here we report the determination of the secondary structure of the rne 5' UTR by phylogenetic comparison and chemical alkylation, together with dissection studies to identify the 5' UTR element that mediates autoregulation. Our findings reveal that the structure and function of the rne 5' UTRs are evolutionarily well conserved despite extensive sequence divergence. Within the rne 5' UTRs are multiple RNA secondary structure elements, two of which function in cis to mediate feedback regulation of rne gene expression. The more potent of these two elements is a stem-loop structure containing an internal loop whose sequence is the most highly conserved of any region of the rne 5' UTR. Our data show that this stem-loop functions as a sensor of cellular RNase E activity that directs autoregulation by modulating the degradation rate of rne mRNA in response to changes in RNase E activity.

5' Untranslated Regions↗

PubMed1999

Transformation of a type 4 encapsulated strain of Streptococcus pneumoniae.

Streptococcus pneumoniae strain JNR.7/87 is a highly virulent, type 4 encapsulated Gram-positive bacterium whose transformability has not been tested previously, and whose genome is currently being sequenced. The strain was transformed at very low efficiency by addition of exogenous competence-stimulating peptide: However, the efficiency was too low and irreproducible to be useful in many genetic studies. Therefore, the effects on transformation efficiency of changing different components of competence-stimulating peptide-induced transformation have been examined. Screening of growth media was followed by optimization of pre-induction culture acidification, glycine concentration, and induction time. An optimized protocol was developed whereby S. pneumoniae strain JNR.7/87 was transformed reproducibly with a streptomycin resistance (SmR) marker at an efficiency of approximately 10(5) colony forming units per 10(8) cells.

Bacterial Proteins↗

PubMed1999

Importance of a 5' stem-loop for longevity of papA mRNA in Escherichia coli.

High-level expression of the major pilus subunit (PapA) of uropathogenic strains of Escherichia coli results in part from the unusually long lifetime of the mRNA that encodes this protein. Here we report that the longevity of papA mRNA derives in large measure from the protection afforded by its 5' untranslated region. This papA RNA segment can prolong the lifetime of an otherwise short-lived mRNA to which it is fused. In vivo alkylation studies indicate that, in its natural milieu, the papA message begins with a stem-loop structure. This stem-loop is important for the stabilizing effect of the papA 5' untranslated region, as evidenced by the significant acceleration in papA mRNA decay that results from its removal.

5' Untranslated Regions↗

PubMed1991

Structure and function of a bacterial mRNA stabilizer: analysis of the 5' untranslated region of ompA mRNA.

The 5' untranslated region (UTR) of the Escherichia coli ompA transcript functions in vivo as a growth rate-regulated mRNA stabilizer. The secondary structure of this mRNA segment has been determined by a combination of three methods: phylogenetic analysis, in vitro probing with a structure-specific RNase, and methylation by dimethylsulfate in vivo and in vitro. These studies reveal that despite extensive sequence differences, the 5' UTRs of the ompA transcripts of E. coli, Serratia marcescens, and Enterobacter aerogenes can fold in a remarkably similar fashion. Furthermore, the Serratia and Enterobacter ompA 5' UTRs function as effective mRNA stabilizers in E. coli. Stabilization of mRNA by the Serratia ompA 5' UTR is growth rate dependent. These findings indicate that the features of the ompA 5' UTR responsible for its ability to stabilize mRNA in a growth rate-regulated manner are to be found among the structural similarities shared by these diverse evolutionary variants.

Bacterial Outer Membrane Proteins↗