Phosphorylation of threonine in the proline-rich carboxy-terminal region of simian virus 40 large T antigen

The position of phosphothreonine in the predicted primary structure of simian virus 40 large T antigen was determined by different methods. After digestion of large T antigen with trypsin and subsequent two-dimensional peptide mapping, a single peptide containing phosphothreonine could be separated from the bulk of phosphoserine-containing peptides. Its amino acid composition was determined by differential labeling with various amino acids in vivo. The high yield of proline (4.5 mol) within the phosphothreonine peptide indicated that it was derived from the carboxy terminus of large T antigen and had in its unphosphorylated form the sequence Lys-Pro-Pro-Thr-Pro-Pro-Pro-Glu-Pro-Glu-Thr-COOH. A phosphopeptide generated by chymotrypsin could be converted into the tryptic phosphothreonine peptide, indicating that the latter was part of the chymotryptic peptide. The origin of the phosphothreonine-containing peptides was independently confirmed by using an antiserum directed against the carboxy terminus of large T antigen. This serum reacted specifically with the proline-rich, phosphothreonine-containing peptides. Further analysis by partial acid hydrolysis indicated that the internal threonine was phosphorylated. The unusual amino acid composition on both sides of the phosphothreonine and the possible function of this phosphorylation site are discussed.

[Phagocytic ability of blast cells in acute leukemia]

In 31 cases of acute leukaemia in adults the ability of leukaemic cells to phagocytize latex was investigated. This ability was confirmed in nearly all cases of monocytic and myelomonocytic leukaemia, in over 1/3 of cases of myeloblastic leukaemia and in one out of 9 cases of lymphoblastic leukaemia.

[Successful embolectomy of the superior mesenteric artery]

Successful embolectomy of the superior mesenteric artery in a 75-year-old man is reported. The decisive points in early diagnosis are discussed and the specific diagnostic methods for the correct decision are presented. The fulminant evolution of the disease leaves little time in which to decide. Early embolectomy brings about complete cure. It is a life-saving operation and there are no contraindications.

[Richter's syndrome and cervical cancer in the course of a rheumatoid arthritis]

The authors describe a rare case of Richter's syndrome (transition of chronic lymphatic leukaemia into reticulosarcoma) developing during rheumatoid arthritis in a women aged 53 years. Chronic antigenic stimulation and disturbances of interaction between lymphocytes T and B are suggested as a cause of Richter's syndrome.