Protein biosynthesis in cell-free systems prepared from hair follicel tissue of guinea pigs

Hair keratinization in health and disease

The cells of the epidermis and its derivative, the hair follicle, undergo processes of terminal differentiation that involves the synthesis and assembly of classes of protein and enzymes to form the stratum corneum of the epidermis, and the hair fiber and its cuticle. Using genetic linkage and DNA sequencing methods, we now know that mutations in several genes encoding epidermal keratins or a transglutaminase enzyme cause ichthyosis-related diseases. Similar methods have now suggested that mutations in hair keratin genes underlie some cases of monilethrix, and a deficiency in a cuticle lipid metabolizing enzyme causes maple syrup urine disease. It is to be expected that further application of these methods will elucidate the molecular bases of other genetic hair diseases.

In vitro biosynthesis of mouse hair keratins under the direction of follicular RNA

A hair follicle-enriched fraction from neonatal C57BL/6J mouse skin has been obtained by a newly-developed preparative procedure. RNA isolated from this source directs protein synthesis in a cell-free translation system derived from rabbit reticulocytes. Translation products in the molecular weight range of keratins (45,000-70,000 Mr) are encoded by RNA species which sediment at 18S on sucrose density gradients. Proteins of 63K, 59K, 58K, 47K and 46K Mr were identified as keratins on the basis of electrophoretic mobilities identical with authentic hair keratins and by immunoprecipitation with keratin antiserum.

Mammalian epidermal messenger RNA: identification and characterization of the keratin messengers

A messenger RNA fraction which directs the synthesis of epidermal keratins and other skin proteins has been isolated from adult guinea pigs and newborn rats, utilizing techniques designed to minimize degradation by endogenous nucleases. During the initial extraction procedures an inhibitor of translation was identified. This inhibitor could be removed by sedimentation of the RNA through cesium chloride. Electrophoresis of the resulting RNA on denaturing agarose/urea gels indicated that, in addition to 18S and 28S ribosomal RNAs, several minor species ranging in size from 10S to 28S were present. This heterogeneous RNA stimulated the incorporation of radioactive amino acids into protein in a reticulocyte lysate system which had an absolute dependence on added mRNA. A fraction of the RNA was retained on oligo(dT)-cellulose, indicating the presence of poly(adenylic acid) sequences. This poly(A)-rich material was considerably enriched for mRNA activity. Analysis of the products of synthesis indicated that proteins which migrated as keratins in 1- and 2-dimensional electrophoretic systems were major translation products of both the unfractionated material and poly(A)-containing fractions. The minimum sedimentation coefficient of keratin mRNAs was found to be 18S, a value consistent with the molecular weight of the keratin polypeptides.

Arginine transferase activity in homogenates from guinea-pig hair follicles

The transfer of arginine from tRNA to the amino terminal region of acceptor proteins has been demonstrated in postribosomal supernatant from guinea-pig hair follicle homogenate. The reaction has no requirement for template nucleic acids, ATP, GTP, or Mg++, and is unaffected by high concentrations of cycloheximide. It is concluded that the arginine transfer activity of the guinea-pig hair follicle is due to the action of a soluble enzyme similar to the arginine transferases previously described for other mammalian tissues.

Translation of polysomal messenger RNA during epidermal differentiation

Translation in vitro of messenger RNA obtained from preparations of active polysomes isolated from the epidermal basal, spinous, and granular cells of the newborn rat has provided evidence that in the context of differentiation in this tissue, control of protein synthesis is exerted at the level of transcription. The data supporting this hypothesis are reviewed.

Isolation and characterization of epidermal ribosomes

The conditions required for isolation of ribosomal particles from guinea-pig epidermis and half-root cells have been studied. Density-gradient patterns of the ribosomes following isolation from either tissue under a wide variety of conditions are essentially the same. Monomeric ribosomes are the predominant species isolable although polymeric ribosomes and subunits can be identified. The density-gradient pattern is not related to runoff during preparation. Detergent extraction is required for maximal recovery of particles from epidermis or wax-epilated hair roots even without detergent. The yield of ribosomes from both epidermis and hair roots is greatest in buffers with potassium concentrations between 100 and 250mM. Yield is decreased in buffers with magnesium concentrations above 5mM. Activity in an in vitro amino acid-incorporating system is unaffected by potassium concentration and is highest at magnesium concentration of 3mM. Activity of epidermal ribosomes is inhibited by the wax-epilation method while hair root-cell ribosomes are equally active following preparation with either latex or wax. The isolated ribosomal particles are unstable at 4 degrees C.

Protein synthesis of the sponge Geodia cydonium: characterization of the system

The ribosomal population of the sponge Geodia cydonium has been examined. The monosomes have a sedimentation constant of 80 S, the sizes of the subunits are approximately 60 S and 45 S respectively. The polyribosomes contain up to 40 ribosomal units. Cell free protein synthesizing systems (cell homogenate as well as reconstituted system) have been prepared and characterized with respect to Mg(2+), KCI and ATP concentrations, temperature, pH and time course of the reaction. In the cell-free system and in the cellular system the protein biosynthesis is inhibited by chloramphenicol. It is not affected by cycloheximide.