Native intermediate filament (IF) preparations from the baby hamster kidney fibroblastic cell line (BHK-21) contain a number of minor polypeptides in addition to the IF structural subunit proteins desmin, a 54,000-mol-wt protein, and vimentin, a 55,000-mol-wt protein. A rnonoclonal antibody was produced that reacted exclusively with a high molecular weight (300,000) protein representative of these minor proteins. Immunological methods and comparative peptide mapping techniques demonstrated that the 300,000-mol-wt species was biochemically distinct from the 54,000-and 55,000-mol-wt proteins. Double-label immunofluorescence observations on spread BHK cells using this monoclonal antibody and a rabbit polyclonal antibody directed against the 54,000-and 55,000-mol-wt proteins showed that the 300,000-mol-wt species co-distributed with IF in a fibrous pattern. In cells treated with colchicine or those in the early stages of spreading, double-labeling with these antibodies revealed the co-existence of the respective antigens in the juxtanuclear cap of IF that is characteristic of cells in these physiological states. After colchicine removal, or in the late stages of cell spreading, the 300,000-mol-wt species and the IF subunits redistributed to their normal, highly coincident cytoplasmic patterns.Ultrastructural localization by the immunogold technique using the monoclonal antibody supported the light microscopic findings in that the 300,O00-mol-wt species was associated with IF in the several physiological and morphological cell states investigated. The gold particle pattern was less intimately associated with IF than that defined by anti-54/55 and was one of non-uniform distribution along IF, being clustered primarily at points of proximity between IF, where an amorphous, proteinaceous material was often the labeled element. Occasionally, "bridges" of label were seen extending outward from such clusters on IF. Gold particles were infrequently bound to microtubules, microfilaments, or other cellular organelles, and when so, IF were usually contiguous. During multiple cycles of in vitro disassembly/assembly of the IF from native preparations, the 300,000-mol-wt protein remained in the fraction containing the 54,000-and 55,000-mol-wt structural subunits, whether the latter were in the soluble state or pelleted as formed filaments. In keeping with the nomenclature developed for the microtubule-associated proteins (MAPs), the acronym IFAP-3OOK (intermediate filament associated protein) is proposed for this molecule.

Thirty nine cadaver elbows were dissected and the branching of the ulnar nerve, as well as the cubital tunnel and adjacent potential sites of nerve compression were studied. An arcade of Struthers was present in 26 specimens and Osborne's ligament was present in all specimens. A discrete flexor pronator aponeurosis overlying the ulnar nerve was present in 17 specimens. An average of one (range, 0-3) capsular nerve branches were noted. These originated an average 7 mm proximal (range, 45 mm proximal to 24 mm distal) to the medial epicondyle. An average of three (range, 1-6) motor branches to the flexor carpi ulnaris muscle were noted, and one of these originated proximal to the medial epicondyle in two specimens. Significant variation was noted in the capsular and motor branching of the ulnar nerve. Care must be taken to identify the motor branches of the ulnar nerve when performing a transposition.

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