The Nucleotide Sequence at the 5′-Terminus of the Qβ RNA Minus Strand

The sequence of the first 52 nucleotides at the 5'-end of the Qbeta minus strand has been determined and found to be complementary in an antiparallel fashion to the 3'-terminal region of the Qbeta plus strand. There are few similarities between the corresponding sequences of Qbeta plus and minus strands; however, both have a hydrogen-bonded loop close to the 5'-end. The sequence of the 3'-terminal region of the plus strand was deduced: there are no termination signals within the last 32 nucleotides. A notable homology exists between the 3'-ends of Qbeta and R17 RNA.     

CHANGES IN CONNECTIVE TISSUE AND INTESTINE CAUSED BY VITAMIN A IN AMPHIBIA, AND THEIR ACCELERATION BY HYDROCORTISONE

In view of the theory that an excess of vitamin A causes release of cathepsins from intracellular lysosomes, hypervitaminosis A was induced orally in the larvae of Xenopus laevis. It was predicted that the tails of these amphibia would undergo resorption prior to metamorphosis, since the presence of abundant lysosomes, associated with measurable increases of catheptic activity, had previously been demonstrated in the resorbing tails of amphibia during metamorphosis. This prediction was confirmed; after 3 to 4 weeks of hypervitaminosis A, the tails of treated animals underwent partial resorption. Other transitory appendages, the rostral tentacles, collapsed after 2 weeks of treatment with an excess of vitamin A, an effect analogous to the collapse of rabbits' ears after intravenous papain. These effects were related to the loss of metachromatic extracellular material in these appendages. Excess of vitamin A caused kyphoscoliosis and prognathos in the larvae. The hypervitaminotic larvae always developed a mucinous diarrhea, which was associated with a remarkable overgrowth of metachromatic goblet cells of the intestine. The entire intestine of the treated animals was more advanced in development than that of control larvae at equivalent stages. All the effects of hypervitaminosis A were accelerated by the simultaneous administration of hydrocortisone. This was held to be due to liberation of vitamin A from hepatic stores by the steroid, and is in contrast to the retardation of hypervitaminosis A by hydrocortisone in vitro.     

The intervening sequence of a mouse beta-globin gene is transcribed within the 15S beta-globin mRNA precursor.

Mouse beta-globin in encoded in a discontinuous structural gene interrupted by a 550-base pair intervening sequence of DNA. Correspondingly, the mature beta-globin mRNA appears to be synthesized via a 15S precursor, the length of which roughly equals the total length of the coding and intervening sequences of the beta-globin gene. Using the electron microscope to visualize hybrid structures formed between this gene and the purified 15S beta-globin mRNA precursor, we show that the intervening sequence is present within the larger precursor molecule. This finding suggests that the precursor mRNA is processed through the removal and rejoining of internal RNA sequences.