title: Noncytotoxic orange and red/green derivatives of DsRed-Express2 for whole-cell labeling.
abstract: BACKGROUND
  Whole-cell labeling is a common application of fluorescent proteins (FPs), but many red and orange FPs exhibit cytotoxicity that limits their use as whole-cell labels. Recently, a tetrameric red FP called DsRed-Express2 was engineered for enhanced solubility and was shown to be noncytotoxic in bacterial and mammalian cells. Our goal was to create derivatives of this protein with different spectral properties.
  
  
  RESULTS
  Building on previous studies of DsRed mutants, we created two DsRed-Express2 derivatives: E2-Orange, an orange FP, and E2-Red/Green, a dual-color FP with both red and green emission. We show that these new FPs retain the low cytotoxicity of DsRed-Express2. In addition, we show that these new FPs are useful as second or third colors for flow cytometry and fluorescence microscopy.
  
  
  CONCLUSIONS
  E2-Orange and E2-Red/Green will facilitate the production of healthy, stably fluorescent cell lines and transgenic organisms for multi-color labeling studies.
authors.affiliation: Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois 60637, USA. strackr@uchicago.edu
authors.forename: Rita L
authors.initials: RL
authors.lastname: Strack
authors.forename: Dibyendu
authors.initials: D
authors.lastname: Bhattacharyya
authors.forename: Benjamin S
authors.initials: BS
authors.lastname: Glick
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Keenan