Presence of prolactin-like immunoreactivity and bioactivity in rat spinal cord.

Pursuant to our identification of prolactin-like immunoreactivity (PLI), widely distributed in rat brain, the spinal cord was examined for the presence of this pituitary-hormone-like protein. PLI was present in all spinal cord extracts examined and averaged 500 +/- 53 pg/mg protein. Hypophysectomy, causing a fall in serum prolactin to undetectable levels, was not associated with any change in levels of PLI in spinal cord. Recovery of rat prolactin standards added to spinal cord homogenates was 97.6 +/- 3.9%. When increasing concentrations of spinal cord extract were assayed in a prolactin radioimmunoassay, displacement of rat 125I-Prolactin from antiserum was parallel to that displacement produced by increasing concentrations of rat anterior pituitary standards. Upon subjection to gel permeation chromatography, the elution profiles of immunoreactive prolactin from spinal cord were different from the profiles of anterior pituitary prolactin. In addition to an immunoreactive prolactin peak eluting with pituitary prolactin, spinal cord extracts showed a large void volume peak and late eluting low-molecular-weight materials not seen with anterior pituitary. In the Nb2 lymphoma cell assay, all spinal cord extracts demonstrated prolactin-like bioactivity with a bioactivity/immunoreactivity ratio of 1.05 +/- 0.13. We conclude: (1) PLI, widely distributed in rat brain, is also present in spinal cord; (2) spinal cord prolactin levels are independent of levels in pituitary and peripheral circulation; (3) this immunoreactive prolactin is bioactive, and (4) differing gel permeation chromatographic elution profiles indicate that there may be some molecular differences between pituitary and spinal cord prolactin.

R-plasmid-mediated chromosomal gene transfer in Agrobacterium tumefaciens.

Although several techniques are available for transferring the Ti plasmids from one strain of agrobacterium tumefaciens to another, there are no reproducible methods for analysis of chromosomal markers in this phytopathogen. The R plasmid, R68.45, is known to show chromosomal mobilizing ability in several bacterial genera including the closely related Rhizobia. R68.45 was transferred into the prototrophic A. tumefaciens strain 15955. Ten kanamycin-resistant transconjugant clones were tested for chromosomal mobilizing ability by mating with strain SA10, rifampin- and streptomycin-resistant histidine auxotroph of strain 15955. Of the 10 donor clones, 2 showed high chromosomal mobilizing ability. Between 1,000 and 2,000 His+ colony-forming units per ml were obtained, a value 10 to 20 times greater than can be accounted for by spontaneous reversion. Sequential recloning and matings resulted in the isolation of relatively stable donor cultures. Chromosome gene transfer is dependent upon the presence in the donor of R68.45. Donors lacking an R plasmid or harboring the closely related plasmid RP4 failed to yield His+ transconjugants. With strain SA11, a methionine auxotroph of strain SA10, coinheritance of histidine and methionine independence could be demonstrated. Approximately half of the transconjugants also inherited R68.45. These results indicate that A. tumefaciens 15955 is capable of undergoing host chromosomal genetic exchange.