1HighYield T7 Atto488 RNA Labeling Kit (UTP-based) is designed to produce randomly Atto488-modified RNA probes via in vitro transcription. Such probes are ideally suited for in situ hybridization and Northern Blot experiments. UTP-ATTO-488 is efficiently incorporated into RNA as substitute for its natural counterpart UTP using an optimized reaction buffer and T7 RNA Labeling Polymerase Mix. ATTO488 possesses, in contrast to Fluorescein, a excellent photostability. 35 % UTP-ATTO-488 substitution typically results in an optimal balance between reaction and labeling efficiency. Individual optimization of UTP-ATTO-488/UTP ratio however, can easily be achieved with the single nucleotide format. The resulting Atto488-modified RNA probe can subsequently be detected by fluorescence spectroscopy. The kit contains sufficient reagents for 20 labeling reactions of 20 μl each (35 % UTP-ATTO-488 substitution, 2.5 mM ATP, GTP, CTP, 0.2 mM UTP, 0.1 mM UTP-ATTO-488).