Calcium activated gene transcription through Nuclear Factor of Activated 
T-cells, (NFAT) proteins, is emerging as a ubiquitous mechanism for the control 
of important physiological processes. Of the five mammalian NFAT isoforms, 
transcriptional activities of NFATs 1-4 are stimulated by a calcium driven 
association between the ubiquitous phosphatase calcineurin and the 
calcium-sensing protein calmodulin. Published in vitro evidence has suggested 
that other members of the calmodulin super-family, in particular the neuronal 
calcium sensor (NCS) proteins, can similarly modulate calcineurin activity. In 
this study we have assessed the ability of NCS proteins to interact directly 
with calcineurin in vitro and report a specific if weak association between 
various NCS proteins and the phosphatase. In an extension to these analyses we 
have also examined the effects of over-expression of NCS-1 or NCS-1 mutants on 
calcineurin signalling in HeLa cells in experiments examining the 
dephosphorylation of an NFAT-GFP reporter construct as a readout of calcineurin 
activity. Results from these experiments indicate that NCS-1 was not able to 
detectably modulate calcineurin/NFAT signalling in a live mammalian cell system, 
findings that are consistent with the idea that calmodulin and not NCS-1 or 
other NCS family proteins is the physiologically relevant modulator of 
calcineurin activity.