A nucleoside/tide compound having the structureNUC--L--S--LB/LGis described wherein NUC is a nucleoside/tide having a nucleobase portion B, L is a rigid linkage, S is a spacer; and LB/LG is a member of a linkage pair or a label. NUC is attached to L through B such that when B is a purine, L is attached to the 8-position of the purine, when B is 7-deazapurine, L is attached to the 7-position of the 7-deazapurine, and when B is pyrimidine, L is attached to the 5-position of the pyrimidine. In an important aspect of the invention, L has the structure ##STR1## wherein each of n, o and p are integers ranging from 0 to 3, and the sum of n, o and p is at least 2, and each of W, X, Y and Z is selected from the group consisting of carbon and nitrogen. The invention further includes polynucleotide compounds comprising the nucleoside/tide, and primer extension methods utilizing the nucleoside/tide, particularly when used in combination with certain mutant polymerase enzymes.