We have shown that the second intron of the Podospora mitochondrial gene coding for cytochrome b (Cytb 12) splices autocatalytically, using in vitro transcripts generated from the T7 promoter. The reaction takes place at 37 degrees C in the presence of 50 mM TRIS-HCl pH 7.5, 60 mM MgCl2 and 1 mM GTP but shows a low efficiency even at high KCl concentrations of up to 1.2 M. Under these conditions, intron bI2 follows the conventional pathway of group I splicing, and all characteristic products, with regard to both transesterification and hydrolysis, could be identified. Moreover, the intron is capable of undergoing cyclization, thereby releasing the noncoded G and one additional nucleotide (U) from the 5' end. The 5' cleavage site is preceded by the same two nucleotides, indicating a base-pairing at the same site of the internal guide sequence (IGS) for both splicing and cyclization ("one-binding-site model"). In addition, products resulting from site-specific hydrolysis 138 nucleotides downstream of the 5' splice site were detected. Unusually, the shortened intron is also able to form a circular RNA and an alternative sequence that aligns the cyclization site to the catalytic core of the intron must be assumed.

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Using 44 anti-O sera 789 Escherichia coli strains isolated from the urine of patients with urinary tract infections were typed. Of the 119 E. coli strains from the urine of children, 49.6% were O-typable; only 3.4% were rough strains. Of 357 strains from pregnant women, 47% were O-typable; 12.1% were rough strains. The largest proportion of O-typable E. coli strains was found among 314 strains isolated from adults with recurrent urinary tract infections (55.4% of the 314 strains); 8% were rough strains. The higher proportion of E. coli rough strains in adults, including pregnant women, indicate that once a pyelonephritis process has been established by virulent smooth strains in childhood, it can be sustained by rough strains at a later stage. Certain O serotypes were found to occur with a variable frequency in the individual patient groups. Enteropathogenic E. coli strains were seldom found in any of the three groups.

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