Isolation and partial characterization of a corynebacteriophage beta, tox operator constitutive-like mutant lysogen of Corynebacterium diphtheriae.

We have isolated and partially characterized a beta-phage mutant lysogen of Corynebacterium diphtheriae, C7(betatoxct1+), which is partially insensitive to iron inhibition of diphtheria toxin production. tox expression by C7(betatoxct1+) was found to be partially constitutive. In the presence of concentrations of iron that almost completely inhibit the expression of diphtheria toxin by the wild type, C7(beta), the level of toxin production by C7(betatoxct1+) was found to be at least 25 times that of the parent. The purified tox gene product of C7(betatoxct1+) was immunologically and electrophoretically identical to, and equally as toxic as, diphtheria toxin purified from C7(beta). In addition, the partial N-terminal amino acid sequence was found to be identical to diphtheria toxin. This data strongly suggests that the mutation allowing for the constitutive expression of tox in C7(betatoxct1+) is outside of the structural gene. Furthermore, the constitutive expression of diphtheria toxin was found to be cis dominant in the double lysogen C7(betacrm45+/betatoxct1+). The data presented is consistent with the existence of a tox operator locus.     

Morphological characterization of tendon development during chick embryogenesis: measurement of birefringence retardation

Morphological observations and physical measurement of (I) birefringence retardation, (2) mean fibre profile width, and (3) cell volume fraction were used to characterize chick hind limb extensor tendon development. Observations were made at days 7, 10, 14 and 17 embryologic and 1-1.5 post-hatching. Microanatomical observations illustrated a sequential development of tendon microanatomy consisting of (1) a uniaxial cellular framework with discontinuous collagen fibril bundles present in day 7 embryos; (2) a continuous network of birefringent collagen fibres, and early evidence of tendon fasciculation and crimp development by embryonic day 10; and (3) completion of the basic cytoarchitecture of tendon observed at day 14 of embryogenesis. These observations suggest that collagen deposition in tendon involves first a longitudinal and then a lateral organization of tendon fibroblasts. Associated with the progressive anatomical development of tendon was an increase in birefringence retardation, mean collagen fibre profile width, and a decrease in the cell volume fraction. Birefringence retardation per unit thickness, however, did not change. This suggested that the fibril packing density of the fibres remained constant, although the fibres were observed to increase in size. These results indicate that collagen fibrillogenesis in vivo can be quantitatively studied by measurement of the birefringence retardation using polarized light.