Although essential to numerous biotech applications, knowledge of molecular recognition by arginine-rich motifs in live cells remains limited. 1H,15N HSQC and 19F NMR spectroscopies were used to investigate the effects of C-terminal -GRn (n = 1-5) motifs on GB1 interactions in Escherichia coli cells and cell extracts. While the "biologically inert" GB1 yields high-quality in-cell spectra, the -GRn fusions with n = 4 or 5 were undetectable. This result suggests that a tetra-arginine motif is sufficient to drive interactions between a test protein and macromolecules in the E. coli cytoplasm. The inclusion of a 12 residue flexible linker between GB1 and the -GR5 motif did not improve detection of the "inert" domain. In contrast, all of the constructs were detectable in cell lysates and extracts, suggesting that the arginine-mediated complexes were weak. Together these data reveal the significance of weak interactions between short arginine-rich motifs and the E. coli cytoplasm and demonstrate the potential of such motifs to modify protein interactions in living cells. These interactions must be considered in the design of (in vivo) nanoscale assemblies that rely on arginine-rich sequences.