Reiterative copying by E.coli RNA polymerase during transcription initiation of mutant pBR322 tet promoters

The major in vitro transcripts from the tet promoter of pBR322 derivatives pTA22 and pTA33 have heterogeneous 5' ends consisting of variable lengths of oligo(A). Their structure is 5'pppAnU..., where n ranges from 1 to greater than 12, but the template strand can encode at most four A residues at the site of transcription initiation. The abundance of additional A residues at the 5' end of the pTA22 and pTA33 tet transcripts could be reduced by elevating the concentration of UTP, but even at high concentrations (greater than 1 mM) non-cognate A residues were still observed. Aberrant initiation was not artifactual since the major and minor transcripts of the pBR322 tet promoter region, and other transcripts arising from minor promoters on pTA22 or pTA33 DNA all had unique 5' termini. Mixing experiments showed that RNA polymerase did not utilize pppA2-4-OH produced by abortive initiation as primers. The data suggest that the initial nascent RNA chain 'slips' in the 5' direction during elongation opposite T4 on the template strand causing RNA polymerase to reiteratively add A residues to the 5' end of the transcript. The generality and possible significance of this mechanism is discussed.

Enzymatic amplification of human cytomegalovirus sequences by polymerase chain reaction

Polymerase chain reaction (PCR) amplification was used to detect human cytomegalovirus (HCMV) sequences. The fragments selected for amplification were fragments of 130 and 152 base pairs (bp) located at two opposite ends of HCMV strain AD169 EcoRI fragment D. Amplification of the 152-bp DNA was consistently greater than that of the 130-bp DNA. At the optimal Mg2+ concentration of 5 mM, specific PCR amplification of 152-bp DNA with Taq polymerase was sensitive; only one AD169-infected fibroblast cell or 0.01 pg of AD169 fragment D DNA was needed for detection. This specific amplification was also found with various clinical HCMV isolates and peripheral blood cells and urine from patients. In 37 urine samples analyzed simultaneously by PCR and by virus cultivation, identical results were found in 35 samples, while 2 scored positive only by PCR. This suggests that specific amplification of 152-bp DNA is sensitive and can be used for rapid detection of HCMV infections.

Transcription initiation at the tet promoter and effect of mutations

We have identified the startpoint for transcription in vitro of the tetracycline resistance gene (tet) of pBR322 and several deletion and insertion mutations which alter tet promoter structure. Tetracycline resistance in host bacteria correlates qualitatively with the efficiency of DNA fragments from these plasmids to promote tet transcription in vitro. Only in active promoters could we find by computer analysis promoter structures in which the -10 and -35 sequences and the relative spacing of the two regions agree with consensus sequence determinants. These data support the current model of the E. coli promoter sequence. Two promoter mutants gave heterogeneous 5' termini with additional A residues not encoded by the DNA sequence.

Comparative studies of nucleic acid hybridization assay for Listeria in foods

A nucleic acid hybridization assay has been developed for Listeria spp. in dairy foods and environmental samples. The assay is based on detection of unique Listeria 16S rRNA sequences by using a 32P-labeled synthetic DNA probe. Inclusivity and exclusivity of the probe were confirmed with 139 Listeria isolates representing all known species, and 73 non-Listeria bacterial strains. In this paper, we present results from our preliminary studies comparing the hybridization assay with conventional culture on a total of 575 specimens that represent a variety of inoculated and uninoculated foods and environmental samples. The assay, which is done in a filter manifold format after 2 days of cultural enrichment, requires a total assay time of less than 2.5 days. The false-negative rate for all sample groups tested using the GENE-TRAK hybridization assay was less than the rate for culture. Thus, the new assay allows rapid screening of the indicated product groups and provides reliable numerical results.

Hepatocellular adenoma. Its transformation to carcinoma in a user of oral contraceptives

Hepatocellular carcinoma arose in a hepatic adenoma associated with the use of oral contraceptives. Although surgical resection was successful, the patient died of sepsis a month postoperatively. No metastases were found at the time of autopsy. Ultrastructural studies of the tumor showed phospholipidosis suggestive of drug-induced toxicity.

Post-operative deep vein thrombosis incidence in Nigerians

In 450 consecutive Nigerian patients aged 20 and above undergoing elective surgery, the incidence of post-operative deep vein thrombosis using clinical methods was 2.2 per cent. Of these 333 were men and 5 had deep vein thrombosis giving an incidence of 1.5 per cent while 117 were females and 5 had deep thrombosis giving an incidence of 4.3 per cent. This figure is low and appears to agree with the current opinion that post operative deep vein thrombosis is comparatively rare in Africans. This is in contrast to the view expressed by Nwokolo and Ikoku (1967) that thromboembolic disease is more common in Nigeria than in East and Central Africa.