Metabolic stability of glutaraldehyde cross-linked peptide DNA condensates

The stability of peptide DNA condensates was examined after introducing glu taraldehyde to cross-link surface amine groups. A 20 amino acid peptide (CW K18) was used to condense DNA into small (70 nm) condensates. The reaction between glutaraldehyde and peptide DNA condensates was indirectly monitored using a fluorescence-based assay to establish reaction completion in 4-5 h when using glutaraldehyde-to-peptide ratios of 1 to 4 mot equiv. Higher le vels of glutaraldehyde cross-linking led to significant increases in partic le size. The improved stability imparted by glutaraldehyde cross-linking wa s demonstrated by the increased resistance of DNA condensates to shear stre ss induced fragmentation. The cross-linked condensates were also significan tly more resistant to in vitro metabolism by serum endonucleases. A decreas e in the magnitude of transient gene expression was determined for cross-li nked DNA condensates which also resulted in a 10-day steady-state expressio n when cross-linking with 4 mol equiv of glutaraldehyde. The results sugges t that crosslinking DNA condensates may provide a means to alter the time c ourse of transient gene expression by inhibiting DNA metabolism.