Tetrahymena conjugation-induced genes: structure and organization in macro- and micronuclei.

The physical organization of eight Tetrahymena genes active during conjugation (meiosis) was examined in the somatic (macro-) and germinal (micro-) nuclei of this organism. Three of these genes make transcripts that are only detected during meiotic prophase. Southern blot analyses indicated that all genes examined were present in both nuclei. Except for one gene family (pC6), all appeared to be non-repetitive and there were no detectable sequence rearrangements in or near the genes. The exceptional gene was repeated approximately five to seven times and DNA rearrangement occurred in or near each of these copies. A comparison of cDNA and macro- and micronuclear DNA restriction maps indicated that one of the genes (cnj B) contains introns. This is the first report of evidence for introns in a non-ribosomal gene in Tetrahymena. A site specific modification probably due to adenine methylation was seen in the macronuclear copy of another gene (cnj C).

Physical stability of insulin formulations.

Insulin aggregation remains a fundamental obstacle to the long-term application of many insulin infusion systems. We here report the effects of physiologic and nonphysiologic compounds on the aggregation behavior of crystalline zinc insulin (CZI) solutions. Under conditions chosen to simulate the most severe that would be encountered in delivery systems (presence of air, continuous motion, and elevated temperature), both highly purified and regular CZI at 5 U/ml formed turbid gels in 5 days. At concentrations of 100 and 500 U/ml stability was increased with turbid gels forming at 12 and 15 days, respectively. Under identical conditions, 5 U/ml CZI formulations containing the physiologic surfactant lysophosphatidylcholine (0.02%) or the synthetic surfactants SDS (1%), Brij 35 (0.1%), Tween (0.01%), or Triton X (0.01%) retained a transmittance at 540 nm of greater than 96% for 67-150 days. These nonionic and ionic surfactants containing the hydrophobic group, CH3(CH2)N, with N = 7-16, remarkably stabilized CZI formulations while those lacking such groups demonstrated little or no effect. The alcohols glycerol (30-50%) and isopropanol (10-50%) were moderately effective stabilizers. Silicone rubber drastically accelerated aggregation in all but one formulation (1% SDS). Emphasis in this study was placed on the properties of 5-U/ml formulations. Controls run at higher concentrations indicated a positive correlation between concentration and stability. It was concluded that the aggregation of insulin into high-molecular-weight polymers may be inhibited by reducing the effective polarity of the solvent. In this regard, anionic and nonionic surfactants containing appropriately long hydrophobic groups demonstrated the greatest degree of stabilization. Finally, of all the medical grade materials likely to be used in pumps, silicone rubber is the most active in promoting insulin aggregation.