Catalyzes the formation of UDP-glucose, from UTP and glucose 1-phosphate. Is highly specific since it cannot use other NTPs such as dTTP, CTP, ATP, and GTP, and other sugar-1P such as GlcNAc-1P, Gal-1P, and Man-1P, as substrates. Has probably a central and essential role as the substrate supplier for galactolipid synthesis; galactolipids are major constituents of the photosynthetic thylakoid membrane and important for photosynthetic activity. alpha-D-glucose 1-phosphate + H(+) + UTP = diphosphate + UDP-alpha-D-glucose kcat is 28 sec(-1) (at pH 7.5 and 37 degrees Celsius). Complete disruption of this gene could not be achieved, suggesting that the CugP-type UDP-Glc PPase is essential for growth and survival of Synechocystis. The CugP-type UDP-Glc PPase appears to be present in all cyanobacteria, whereas the GalU-type UDP-Glc PPase is present in only certain cyanobacterial species. Moreover, the GalU-type PPase is found to be widely distributed throughout the bacterial kingdom, whereas the CugP-type can be found in only very limited species other than cyanobacteria. Belongs to the CugP-type UDP-glucose pyrophosphorylase family.