Gilles Paradis

High level of expression in the prostate of a human glandular kallikrein mRNA related to prostate-specific antigen.

Using a synthetic oligonucleotide primer complementary to human prostate‐specific antigen mRNA, we found that an additional sequence possibly similar to human glandular kallikrein‐1 could be read by a primer‐extension sequencing technique. We were able to confirm the identity of that additional sequence with another oligonucleotide primer complementary to a specific region of the human glandular kallikrein‐1 mRNA sequence. Northern blot analysis with 2 oligonucleotide probes respectively specific for prostate‐specific antigen and human glandular kallikrein‐1 mRNAs showed that the length of both mRNAs was similar at 1.5 kb. The level of human glandular kallikrein‐1 mRNA relative to that of prostate‐specific antigen could be estimated as approx. 10–20%. This study constitutes the first evidence that the human glandular kallikrein‐1 gene is expressed at a high level in a human tissue.

Phosphorylation of ribosomal proteins S3, L1 and L24 during spherulation in Physarum polycephalum

The phosphate content of ribosomal proteins S3, L1 and L24 has been determined in the course of spherulation of Physarum polycephalum. The major phosphoprotein, S3, was completely dephosphorylated after 4 h of differentiation. The phosphate content of L1 and L24 was not altered during the differentiation. The cellular level of ATP remained constant for at least 5 h. A 3-fold reduction of cyclic AMP concentration occurred in the first hour, followed by a slow increase to a final value of twice the level observed in growing cells. The results showed that the phosphorylation of ribosomal proteins is regulated by at least two different mechanisms and that the dephosphorylation of S3 is not induced by a lack of cellular ATP. Although cyclic AMP might trigger the dephosphorylation of S3, the phosphate content of this protein remained at a very low value even when the cellular concentration of cyclic AMP rose significantly. Since the polysome level remains constant during the first 24 h of spherulation, the phosphorylation of S3 is not necessary for active protein synthesis and the phosphorylation of L1 and L24 is not involved in ribosome inactivation, which occurs after 24 h.

Phosphorylation of ribosomal proteins during the cell cycle of Physarum polycephalum

Physarum polycephalum has been used as a model system to study the phosphorylation of ribosomal proteins during the cell cycle. The results showed that the phosphate content of S3, the major ribosomal phosphoprotein in this organism, was constant during all phases of the cell cycle. No additional ribosomal phosphoproteins were observed. These results differ significantly from those reported earlier by Rupp, R.G., Humphrey, R.M. and Shaeffer, J.R. (Biochim. Biophys. Acta (1976) 418, 81-92) and suggest that the use of thymidine or hydroxyurea to synchronize cell population may affect the phosphorylation of ribosomal proteins. The results are discussed in relation to protein synthesis and cAMP level during the cell cycle.