The duck alpha A globin but not the yeast actin gene is transcribed by a HeLa cell extract.

We have investigated the transcription in a HeLa whole-cell extract of two evolutionary widely separated structural genes coding for duck alpha A globin and yeast actin. Transcription of isolated DNA fragments of the duck alpha A globin gene increases linearly up to relatively high concentrations of DNA. Size analyses and S1 mapping of the transcripts synthesized in vitro on either linear DNA fragments or supercoiled templates reveal that the alpha A globin RNA is initiated at the in vivo cap site and remains unspliced. The same assay conditions were used to transcribe the yeast actin gene. In contrast to the duck gene, size analyses and S1 mapping of the RNA products synthesized on both linear DNA fragments and the supercoiled template containing the actin gene show that the transcripts found in vitro do not stem from the in vivo cap site. The promoter of the yeast actin gene is not recognized in this system in vitro.

Screening for mutants of Rhizobium japonicum with defects in nitrogen fixing ability.

Mutants of Rhizobium japonicum with reduced ex planta nitrogenase activity could be isolated with high frequency by direct screening of ultra-violet mutagenized bacteria growing as spots on the surface of an appropriate agar medium permitting derepression of nitrogenase synthesis. Small glass chambers fitted with a serum cap were pushed into the agar around each spot of growth, forming a small enclosed gas space which was made to 10% acetylene, permitting assessment of nitrogenase activity by the acetylene reduction test. Four mutants were isolated from a total of 305 screened spots. Two mutants had almost no ex planta activity, one of which had no symbiotic activity despite normal nodulation (ineffective), the other had only somewhat reduced activity symbiotically. Two other mutants with less than half wild-type activity ex planta were normal in symbiosis.