Transfection of Escherichia coli spheroplasts. II. Relative infectivity of native, denatured, and renatured lambda, T7, T5, T4, and P22 bacteriophage DNAs

The change of infectivity of phage DNAs after heat and alkali denaturation (and renaturation) was measured. T7 phage DNA infectivity increased 4- to 20-fold after denaturation and decreased to the native level after renaturation. Both the heavy and the light single strand of T7 phage DNA were about five times as infective as native T7 DNA. T4 and P22 phage DNA infectivity increased 4- to 20-fold after denaturation and increased another 10- to 20-fold after renaturation. These data, combined with other authors' results on the relative infectivity of various forms of phiX174 and lambda DNAs give the following consistent pattern of relative infectivity. Covalently closed circular double-stranded DNA, nicked circular double-stranded DNA, and double-stranded DNA with cohesive ends are all equally infective and also most highly infectious for Escherichia coli lysozyme-EDTA spheroplasts; linear or circular single-stranded DNAs are about 1/5 to 1/20 as infective; double-stranded DNAs are only 1/100 as infective. Two exceptions to this pattern were noted: lambda phage DNA lost more than 99% of its infectivity after alkaline denaturation; this infectivity could be fully recovered after renaturation. This behavior can be explained by the special role of the cohesive ends of the phage DNA. T5 phage DNA sometimes showed a transient increase in infectivity at temperatures below the completion of the hyperchròmic shift; at higher temperatures, the infectivity was completely destroyed. T5 DNA denatured in alkali lost more than 99.9% of its infectivity; upon renaturation, infectivity was sometimes recovered. This behavior is interpreted in terms of the model of T5 phage DNA structure proposed by Bujard (1969). The results of the denaturation and renaturation experiments show higher efficiencies of transfection for the following phage DNAs (free of single-strand breaks): T4 renatured DNA at 10(-3) instead of 10(-5) for native DNA; renatured P22 DNA at 3 x 10(-7) instead of 3 x 10(-9) for native DNA; and denatured T7 DNA at 3 x 10(-6) instead of 3 x 10(-7) for native DNA.

Relationship between cardiac output and peripheral resistance in borderline hypertension

Eighty-eight observations on 77 patients with borderline hypertension and 82 single observations in healthy control subjects are reported. Hemodynamic effects of assumption of the sitting position, mild exercise, infusion of dextran, blockade with propranolol and with a combination of propranolol and atropine are evaluated. In the recumbent position, patients with borderline hypertension have increased cardiac output and "normal" peripheral resistance. Under all other experimental conditions, the peripheral resistance in patients with borderline hypertension was elevated. Increased resistance was accompanied by a decrease of the cardiac output. After administration of the atropine and propranolol combination, cardiac output in patients with borderline hypertension was significantly below the normal. Nevertheless, whether cardiac output was high or low and resistance normal or elevated, patients with borderline hypertension maintained mild elevations of the blood pressure. Consequently, borderline hypertension is not caused solely by elevations of cardiac output.