The uptake and metabolism of uridine by the slime mould Physarum polycephalum.

1. Uridine is taken up by microplasmodia of Physarum polycephalum via a saturatable transport system with an apparent Km of 29 muM. An intracellular concentration significantly higher than that in the growth medium is attained, suggesting that the uptake is an active process. Both deoxyribonucleosides and ribonucleosides are competitive inhibitors of the uptake of uridine. 2. In contrast, the rate of entry of uridine into surface plasmodia is a linear function of the concentration of the nucleoside in the growth medium, and the uptake is not inhibited by other nucleosides. 3. As well as serving as a source of pyrimidine nucleotides for the synthesis of nucleic acids, uridine is also catabolised by P. polycephalum. Uracil accumulates in the growth medium and there is also significant conversion of C-2 of the pyrimidine ring to CO2. The proportion of uridine subject to catabolism in surface plasmodia is less than that observed for microplasmodia.     

Rapid amplification and cloning of Tn5 flanking fragments by inverse PCR

A simple approach is described to efficiently amplify DNA sequences flanking transposon Tn5 insertions. The method involves: (i) digestion with a restriction enzyme that cuts within Tn5; (ii) self-ligation under conditions favouring the production of monomeric circles; (iii) four parallel PCR reactions using primers designed to amplify left or right flanking sequences, and to distinguish target amplicons from non-specific products. This reveals the number of Tn5 insertions and the size of flanking genomic restriction fragments, without Southern blot analysis. The amplified product contains restriction sites that facilitate cohesive-end cloning. This rapid method is demonstrated using Tn5 and Tn5-Mob tagged DNA sequences involved in albicidin biosynthesis in Xanthomonas albilineans. It is generally applicable for efficient recovery of DNA sequences flanking transposon Tn5 derivatives in insertional mutagenesis studies.     

Transhepatic Cholangiography

Percutaneous transhepatic cholangiography is a method of visualizing the biliary tree by the injection of radio-opaque medium through the abdominal wall and liver into an intrahepatic bile duct. The procedure is indicated in the immediate preoperative evaluation of patients with obstructive jaundice of unknown etiology and is usually diagnostic in these cases. It may also be of value in avoiding operation in poor-risk patients with obstructive jaundice. Biliary leak resulting in chemical peritonitis is a complication in about 5% of these procedures. Intraperitoneal hemorrhage is a complication in less than 1%. Death results from the procedure in less than 0.5% of cases. Transhepatic cholangiography during surgical operation is of value in demonstrating obstructive lesions of the bile ducts. However, preoperative percutaneous transhepatic cholangiography is preferred, since it makes possible adequate preparation for technically difficult repairs and resections.