The Sun is the only star for which individual surface features can be observed directly. For other stars, the properties of starspots, stellar rotation, stellar flares etc are derived indirectly via variation of star-integrated spectral line profiles or their luminosity measurements. Using solar disk-integrated and disk-resolved observations allows investigating the contribution of individual solar disk features to Sun-as-a-Star spectra. In this talk, we will present recent improvements in observations and data reduction for the Integrated Sunlight Spectrometer (ISS), one of three instruments comprising the Synoptic Optical Long-term Investigations of the Sun (SOLIS) system. The ISS, in operation since late 2006, takes high spectral resolution daily observations of the Sun in nine different wavelength bands centered at 388.40 nm (CN head band), 393.37 nm (Ca II K), 396.85 nm (Ca II H), 538.00 nm (C I), 539.41 nm (Mn I), 589.59 nm (Na I D1), 656.30 nm (Hα), 854.19 nm (Ca II), and 1083.02 nm (He I). We will also discuss the results of two recent studies based on ISS data: the solar cycle variation in the Ca II K basal profile and the signature of solar differential rotation in Sun-as-a-Star spectra.