Biomedical subjects

M Johnsen

Publications and source records attributed to M Johnsen.

23 records · Page 2Linked to original sources

PubMed1984

RNA secondary structure and translation inhibition: analysis of mutants in the rplJ leader.

We have carried out measurements of the stable binding of the ribosomal protein (r-protein) complex L10-L7/L12 to mutant forms of the mRNA leader of the rplJ operon of Escherichia coli. One of the point mutations, base 1548, which lies within the L10-L7/L12-protected region, almost completely abolishes in vitro formation of a stable complex of L10-L7/L12 with rplJ mRNA leader, and a second point mutation, base 1634, strongly reduces it. These observations constitute strong support for the proposition that L10-L7/L12 binds to the rplJ leader in bringing about translational feedback. To account for the action of these and other mutations, and to explain the mechanism of translation feedback inhibition, we suggest a secondary structure model involving alternate forms of the rplJ mRNA leader.

DNA-Directed RNA Polymerases↗

PubMed1982

Autogenous control: ribosomal protein L10-L12 complex binds to the leader sequence of its mRNA.

Ribosomal proteins L10 and L12 are encoded in the L10 operon, situated at position 89.5 min on the Escherichia coli genetic map, and are able to regulate their own translation. The two proteins form a L10-L12 complex that is able to bind specifically to the leader sequence of the L10 operon mRNA and prevent translation. We show that the leader sequence: (i) is required for the translation of mRNA into L10 and L12 proteins; and (ii) contains a unique binding site for the inhibitory L10-L12 complex. We suggest that a specific secondary structure of the leader RNA is required for translation. When this structure is perturbed by L10-L12 binding, by deletion, or point mutations, translation is inhibited. The block on the synthesis of L10 and L12 can presumably be removed by the incorporation of the inhibitory L10-L12 complex into assembling 50S ribosome subunits. We observed that rRNA prevents the binding of L10-L12 to the mRNA. Furthermore, we have identified extended sequence homologies within the 23S rRNA and L10 leader region RNA. The L10-L12 binding site on the mRNA includes part of the homologous sequences.

Bacterial Proteins↗

PubMed1982

Insertions of transposon Tn5 into ribosomal protein PNA polymerase operons.

The genetic organization and interrelationships between the two ribosomal protein transcription units (the L11 and L10 operons) from near 89 min on the Escherichia coli chromosome were studied by using insertional mutations generated by the kanamycin-resistant transposable element Tn5. The polar effects of Tn5 insertions on the expression of the L11, L1, L10, and L12 ribosomal protein genes and the beta RNA polymerase subunit gene were examined (i) by the level of beta-galactosidase activity generated from L10-lacZ and beta-lacZ gene fusions, (ii) by direct sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the proteins specified by plasmid ribosomal protein genes in UV-irradiated maxicells, and (iii) by urea-polyacrylamide gel electrophoresis of plasmid- and chromosome-specified L12 protein. The results confirmed the organization of these genes into two transcription units as follows: PL11, rplK (L11), rplA (L1), PL10, rplJ (L10), rplL (L12), rpoB (beta). . .; they also localized the position of the PL10 promoter within an 80-nucleotide region near the end of the L1 gene. The results also support the idea that the translational regulatory proteins for the L11 and L10 operons are L1 and L10, respectively, and that the expression of the L12 gene is closely linked to L10 gene expression.

Bacterial Proteins↗

PubMedDate not supplied

Multifrequency tympanometry. Preliminary experiences with a commercially available middle-ear analyzer.

Normal ears and ears affected by various pathologies were studied with a clinical middle-ear analyzer according to the multifrequency tympanometric concept, by which the resonance frequency of the tympanic membrane/middle-ear system can be determined. This frequency varies considerably in normal ears with a mean value close to 1 kHz. Ears with pathologies in the tympanic membrane and otosclerotic ears have resonance frequencies differing significantly from those of normal ears. The effects may be explained by considering mass and stiffness components.

Acoustic Impedance Tests↗

PubMedDate not supplied

Theoretical investigation of a phased-array hyperthermia system with movable apertures.

A four-applicator phased-array hyperthermia system with movable apertures (MA) is compared with an eight-applicator annular phased-array hyperthermia system with fixed apertures (AA) in terms of the HEP (hyperthermia equipment performance) values, based on two-dimensional models and the bioheat transfer equation. A hybrid element method is used to calculate the zeta-directed two-dimensional electric field with the inhomogeneities in tissue properties taken into account. The amplitudes and phases of each applicator are then optimized with the objective of uniform power deposition in the tumour and no power deposited in normal tissues. The temperature distributions under different blood flow conditions are obtained by solving the bioheat transfer equation using the finite element method. It is found that among the seven patient models studied, the MA and AA in general perform equally well when the tumour has zero blood flow, or equally poorly when the tumour has a blood flow larger than 5 ml/100 g per min. The performance of AA is often significantly better than that of MA when the tumour blood flow is 2.7 ml/100 g per min. The effects of different weighting functions are evaluated. We show that even if uniform absorbed power density (ARD = absorption rate density) could be achieved in the tumour volume with zero ARD in normal tissue the entire tumour would still not be brought to 43 degrees C or greater. However, it is found that the performance of uniform ARD in the tumour is on average far better than either the AA or MA, and choosing the uniform ARD as the objective function improved 35% of the cases for AA and 16% for MA. The optimization formula includes a weighting function that can be varied for different tissues. By decreasing the weights in regions of high blood flow the HEP values can sometimes be improved quite noticeably. Finally, the importance of the locations of applicators is studied. The results obtained indicate that the applicators should be placed about 5 cm or more away from the patient body (assuming water is the coupling medium) to ensure good HEP ratings.

Blood Flow Velocity↗