The small heat shock protein hsp25 is accumulated in P19 embryonal carcinoma cells and embryonic stem cells of line BLC6 during differentiation

Murine embryonal carcinoma and embryonic stem cell lines were investigated with regard to the occurrence of the small heat shock protein hsp25 during cell growth and differentiation. In the embryonal carcinoma cell line F9 considerable constitutive levels of hsp25 were observed which could be slightly increased by treatment with retinoic acid. No hsp25 was found, however, in the embryonal carcinoma cell line PCC4. When analyzing the pluripotent embryonal carcinoma cell line P19 and the pluripotent embryonic stem cell line BLC6, both characterized by high differentiation capacity, no hsp25 was observed under cell culture conditions maintaining the undifferentiated state. Induction of differentiation caused by prolonged cell culture, retinoic acid treatment, or embryoid body formation, however, resulted in an increase of the level of hsp25. The finding that hsp25 is accumulated in a differentiation-dependent manner suggests that this protein is associated with processes involved in differentiation. Therefore, hsp25 can be regarded as a marker of differentiation in the investigated embryonal carcinoma cell line P19 and the embryonic stem cell line BLC6.     

Structure of initiation factor eIF-3 from rat liver. Hydrodynamic and electron microscopic investigations

On the basis of hydrodynamic, electron microscopic and biochemical investigations a new model of the structure of initiation factor eIF-3 is proposed. From sedimentation and diffusion coefficients of 16.35 S and 2.13 X 10(-7) cm2/s, respectively, as well as from sedimentation equilibrium measurements, a molecular mass of about 650 kDa was determined for isolated eIF-3. This is in agreement with molecular mass estimations by sodium dodecyl sulphate gel electrophoresis. A partial specific volume of 0.723 cm3/g was determined by means of the amino acid composition and the specific volume increments of the amino acids. From this value and from the molecular mass, a volume of 780 nm3 was calculated for eIF-3. In electron micrographs of isolated eIF-3, images with triangular profiles and side lengths of 14 nm, 16 nm, and 17 nm have been observed. Taking into account the calculated volume and considering the triangular image as one face of the particle, it is suggested that eIF-3 has the shape of a flat triangular prism with a height of about 7 nm and the above-mentioned side-lengths. This model is in agreement with results of electron microscopic investigations of eIF-3 in native small ribosomal subunits [Lutsch, G., Benndorf, R., Westermann, P., Bommer, U.-A. & Bielka, H. (1986) Eur. J. Cell Biol. 40/2, in press]. The high frictional ratio of about 1.7 also supports eIF-3 to be rather of a flat than of a globular shape.