In the midst of this process, the researchers noticed one of the chromosome carriers that wanders the spindle -- the motor protein CENP-E -- and focused their attention on it; additionally, the researchers selectively added and removed, in different experiments, a signal from the microtubules, tyrosine. Helder Maiato explains that "whenever we change the signals across the microtubules, there is a major shift in the way chromosomes circulate." If every microtubule is signaled with tyrosine, the chromosomes will come to a halt near the centrosomes," the roundabouts in our analogy. If, on the contrary, the whole mitotic spindle is stripped of every tyrosine signal, the chromosomes go beyond the poles and get off-track in the secondary roads. The researcher explains that "if the microtubule has traces of tyrosine, the CENP-E carrier rests and doesn't transport any chromosomes from the pole; but should the microtubules have no tyrosine signal, as it happens with the system's main microtubules, the CENP-E tows the chromosomes to the spindle equator.