Alan Munro

Control of haemoglobin synthesis: Rate of translation of the messenger RNA for the α and β chains

Abstract The rates of translation of the messenger RNA for the α and β chains of rabbit globin have been measured, and it is found that the α chain is translated faster than the β chain. This means that two different classes of messenger RNA are translated at different rates within the same cells.

Control of haemoglobin synthesis: Distribution of ribosomes on the messenger RNA for α and β chains

The nascent peptides attached to the polysomes of rabbit reticulocytes were labelled with [3H]lysine, and the specific activity of the tryptic peptides derived from them measured. The data show that ribosomes are uniformly distributed on mRNA when the cells are incubated under standard in vitro conditions. When cells were incubated in the absence of tryptophan, or when they were exposed briefly to sodium fluoride after the nascent peptides had been labelled, the ribosomes were found at one or other end of the mRNA. From the uniform distribution of the nascent chains in normally incubated cells we conclude that the rate of movement of the ribosomes over all regions of the mRNA is uniform. We are able to deduce the relative number of ribosomes carrying nascent α and β chains. The number of complete chains isolated with the ribosomes varied from 17 to 160 complete chain/nascent chains. In no case was an excess of complete α chains over β chains found attached to the ribosomes. These results are discussed in relation to the rate limiting step in the assembly of globin.

Immunoglobulin biosynthesis. I. A myeloma variant secreting light chain only.

Abstract A mutant mouse myeloma cell line was derived from ADJPC5, which secretes an IgG 2a immunoglobulin. The variant had lost the ability to synthesize immunoglobulin, but continued to secrete light chain. This light chain, and the light chain from ADJPC5 immunoglobulin, were indistinguishable as defined by peptide mapping of the secreted serum, and urinary proteins. Karyotype analysis showed that the mutant was derived from one of the 14 stem-lines observed in the wildtype myeloma. There was no detectable internal immunoglobulin in the variant, ruling out a block in secretion. It was also shown that the differential rate of light chain secretion was identical in ADJPC5 and its derivative.