Unexpected structural diversity in DNA recombination: the restriction endonuclease connection

Transposition requires a coordinated series of DNA breakage and joining reactions. The Tn7 transposase contains two proteins: TnsA, which carries out DNA breakage at the 5' ends of the transposon, and TnsB, which carries out breakage and joining at the 3' ends of the transposon. TnsB is a member of the retroviral integrase superfamily whose hallmark is a conserved DDE motif. We report here the structure of TnsA at 2.4 A resolution. Surprisingly, the TnsA fold is that of a type II restriction endonuclease. Thus, Tn7 transposition involves a collaboration between polypeptides, one containing a DDE motif and one that does not. This result indicates that the range of biological processes that utilize restriction enzyme-like folds also includes DNA transposition.

Fine needle aspiration cytologic diagnosis of axillary accessory breast tissue, including its physiologic changes and pathologic lesions

Sixty-nine cases of axillary accessory breast tissue, including its physiologic changes and pathologic lesions, were diagnosed by fine needle aspiration cytology. The age of the patients ranged from 13 to 40 years, with a median of 25, and all were female. The cases presented with swellings in the left axilla in 16 cases, right axilla in 30 cases and both axillae in 23 cases. The common clinical diagnoses included accessory breast tissue (23.2%), lipomatous lesion (17.4%), lymphadenopathy (18.8%) and swellings not otherwise specified (30.4%). In 8.8% cases two of the possibilities were considered. The cytodiagnoses included axillary accessory breast tissue (47 cases), axillary breast tissue with pregnancy or lactational changes (15), cystic disease (4) and fibroadenoma (3). One of the cystic disease cases showed granulomatous inflammation. Although no case of carcinoma in axillary breast tissue was diagnosed during the study period, there were two cases of malignancy in axillary swellings (diagnosed as metastatic carcinoma) when no primary was detected in the breasts.