The green fluorescent protein (GFP) of Aequorea victoria is a unique i
n vivo reporter for monitoring dynamic processes in cells or organisms
, As a fusion tag GFP can be used to localize proteins, to follow thei
r movement or to study the dynamics of the subcellular compartments to
which these proteins are targeted. Recent studies where GFP technolog
y has revealed new insights regarding physiological activities of livi
ng cells are discussed.