Nuclear Distribution of Prothymosin α and Parathymosin: Evidence That Prothymosin α Is Associated with RNA Synthesis Processing and Parathymosin with Early DNA Replication

• Published in: Experimental cell research 2000-05, Vol.257 (1), p.152-161
• Main Authors: Vareli, Katerina, Frangou-Lazaridis, Maria, van der Kraan, Ineke, Tsolas, Orestes, van Driel, Roel
• Format: Article
• Language: English
• Subjects: Cell Nucleus - genetics; Cell Nucleus - metabolism; DNA Replication; Humans; nuclear bodies; parathymosin; PML bodies; Protein Precursors - metabolism; prothymosin α; RNA - biosynthesis; RNA processing; Thymosin - analogs & derivatives; Thymosin - metabolism; transcription; Tumor Cells, Cultured
• ISSN: 0014-4827; 1090-2422
• DOI: 10.1006/excr.2000.4857

Prothymosin α and parathymosin are two ubiquitous small acidic nuclear proteins that are thought to be involved in cell cycle progression, proliferation, and cell differentiation. In an effort to investigate the molecular function of the two proteins, we studied their spatial distribution by indirect immunofluorescence labeling and confocal scanning laser microscopy in relation to nuclear components involved in transcription, translation, and splicing. Results indicate that both proteins exhibit a punctuated nuclear distribution and are excluded by nucleoli. The distribution of prothymosin α in the nucleus is related to that of transcription sites, whereas the distribution of parathymosin correlates with early replication sites. This implies that prothymosin α and parathymosin are involved in transcription and replication, respectively. In addition to the punctate distribution, prothymosin α also is found concentrated in 1–6 nuclear domains per cell. These domains are found in more than 80% of randomly growing T24 human bladder carcinoma cells. They have a diameter of 0.2–2.5 μm, their size being inversely related to the number of domains per cell. The domains disappear during mitosis and the protein is excluded from the metaphase chromosomes. Double-labeling experiments associate these prothymosin α domains with PML and CstF64 containing nuclear bodies, but not with hnRNP-I containing domains or coiled bodies.