Fragments comprising the 49 nucleotides from the 3′-end have been purified from 16s ribosomal RNA of wild-type Esoheriohia coli and from a kasugamycin-resistant mutant that specifically lacks ...dimethylation of two adjacent adenines near the 3′-terminus. These fragments, obtained after treatment of ribosomes in vitro with the bacteriocin cloacin DF13, were used to study the effect of the methylgroups on the temperature dependent unfolding of double-stranded regions. Both fragments contain at least 3 independent melting transitions, of which the one with the highest Tm corresponds with the unfolding of a nine-basepair long central hairpin. Dimethylation of the adenines in the loop of this hairpin lowers the melting temperature (Tm) by approximately 2°C at 0.2 M NaCl and by about 5°C at 0.015 M NaCl. It is suggested that m26Am26A is more antagonistic to loop formation than ApA and that the function of the methylgroups is to help to destabilize the 3′-terminal hairpin in 16S rRNA in order to facilitate intermolecular interactions.
From 1975 to 1990 we performed subtalar or triple arthrodesis on 54 patients; 48 of them were reviewed after a mean follow-up of 10 years (6 to 15). There were 17 subtalar fusions in 14 patients and ...37 triple arthrodeses in 28 patients. We assessed tibiotalar ankle function using the criteria of Mazur which gives a points score of a maximum of 100. Radiological evidence of degenerative change was graded on a scale of 0 to 4. The mean Mazur score was 85 for the subtalar fusions and 78 for the triple arthrodeses. The radiological score showed no degenerative changes in 36 feet (24 triple and 12 subtalar arthrodeses) and an increase of one grade in 14 feet (10 triple and 4 subtalar), of two grades in three feet (all triple arthrodeses) and of three grades in one foot after a subtalar arthrodesis. We found no statistically significant difference in the radiological score in unilateral fusions between feet with subtalar and triple arthrodeses and the contralateral foot. In all four feet which showed an increase in degenerative changes of two or more grades, there was an abnormality of the tibiotalar joint before the fusion operation. Of the 14 feet which showed an increase of one grade, there was a similar increase on the contralateral side in nine. Our findings show that subtalar or triple arthrodesis has little adverse influence on the function of the tibiotalar joint, even after many years.
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