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their data compared with regional norms and industry standards currently derived from 1979 data.Mortality figures for the north central region of 0.21% and for the entire United States of 0.20% in QAM closely match that reported by Detmer et al (0.17%). The patients with normal tissue in the QAM data for the north central region, 9.91%, and the entire United States, 9.14%, indi¬ cate there may be room for decreases in the negative appendectomy rates, as the authors conclude. The postop¬ erative complication rates for the north central region and the entire United States of 3.21% and 3.34%, respectively, in QAM also is at vari¬ ance with the 5.3% reported in the Wisconsin study. The discrepancy may be due, however, to differences in the definition of complication.These data are presented in support of the authors' contention that hospi¬ tal data can provide the hospital's medical staff with useful information to monitor, correct, or justify their own performance. We maintain that the industry standards developed for that purpose be established from a broader base of regional data and even from a national base when rea¬ sonable. Only then will reductions in variance of performance between hos¬ pitals be possible. Volume To the Editor.\p=m-\In the article by Charles A. Hall, MD (1981;245:1144), we do not dispute the fact that a high mean corpuscular volume (MCV) (normal range, 78 to 93 femtoliters [fL]) should alert a physician to the possibility of vitamin B12 or folate deficiency; however, there are a multitude of other important causes of high MCV, some of which are liver disease, renal disease, hypothyroidism, blood regeneration, and malaria, to name a few.1 In our experience, which consists of a study of the vitamin B12 status of 772 patients during a two-year period, 101 (13%) were found to have a low serum vitamin B12 level. Of these 101patients only four were found to have a high MCV (greater than 93 fL).Conversely, in 45 patients of the 772 studied who had a high MCV, only five (11%) had a low vitamin B12 serum level.The folate status of these patients has also been investigated by serum folate and RBC folate estimations.The following are our findings.1. In 766 patients, serum folate levels were determined, of which 169 were low (less than 4 nmole/L). In this group of 169, only 15 (9%) had high MCVs.2. Within this group of 766, fortysix had high MCVs while only 12 (26% ) of these patients had a low serum folate level.3. Red blood cell folates were per¬ formed in 603 patients, 164 of which were low (less than 450 nmole/L); of these 164, only 12 (7%) had high MCVs.4. Furthermore, of the group of 603, thirty had high MCVs, and only 13 (43%) had low RBC folate levels.Thus, in our experience, we do not consider that a high MCV is a reliable screening test in vitamin B12 or folate deficiency.Furthermore, Dr Hall states that "pernicious anemia is an uncommon disease." However, in the geriatric community in which we practice, we have found that pernicious anemia is relatively common (2%) as compared with the commun...

N-terminal bundle of Vh establish that the structure of this domain is regulated by contacts with cytoskeletal proteins. For example, the binding of talin between helices a1 and a2 displaces Vt, and a-actinin binding to Vh also displaces Vt, yet talin and a-actinin bind to Vh in a mutually restricted manner. The exclusive interactions of these a-helices with Vh would thus serve to properly direct cytoskeletal and signalling decisions induced by focal adhesions versus adherens junctions (Fig. 5). The remarkable structural changes in the a-helices of the Nterminal bundle of Vh establish helical bundle conversion as a mechanism of control in signal transduction pathways. Helical bundle conversion is fundamentally different from helical exchange, where the binding of one a-helix simply displaces the binding of another without altering the structure of the displaced helix (Supplementary Fig. S4). Rather, helical bundle conversion provokes dramatic changes in the conformation of a-helices, allowing proteins to expand their repertoire of structures, substrates and functions. A Methods Detailed information on methodological aspects of X-ray data collection, structure determination and refinement is provided as Supplementary Information.